Merge pull request #5 from ferdzo/feature/auth

Authentication

.env.example

@@ -7,3 +7,14 @@ ADDRESS=0.0.0.0
 GC_INTERVAL=10
 GC_ENABLED=true
 MULTIPART_RETENTION_HOURS=24
+AUTH_ENABLED=false
+AUTH_REGION=us-east-1
+AUTH_SKEW_SECONDS=300
+AUTH_MAX_PRESIGN_SECONDS=86400
+# When AUTH_ENABLED=true you MUST set AUTH_MASTER_KEY to a strong random value, e.g.:
+#   openssl rand -base64 32
+AUTH_MASTER_KEY=REPLACE_WITH_SECURE_RANDOM_KEY
+AUTH_BOOTSTRAP_ACCESS_KEY=
+AUTH_BOOTSTRAP_SECRET_KEY=
+AUTH_BOOTSTRAP_POLICY=
+ADMIN_API_ENABLED=true

README.md

@@ -29,13 +29,40 @@ Multi-object delete:
 
 AWS SigV4 streaming payload decoding for uploads (`aws-chunked` request bodies)
 
+Authentication:
+- AWS SigV4 request verification (header and presigned URL forms)
+- Local credential/policy store in bbolt
+- Bootstrap access key/secret via environment variables
+
+Admin API (JSON):
+- `POST /_admin/v1/users`
+- `GET /_admin/v1/users`
+- `GET /_admin/v1/users/{accessKeyId}`
+- `PUT /_admin/v1/users/{accessKeyId}/policy`
+- `PUT /_admin/v1/users/{accessKeyId}/status`
+- `DELETE /_admin/v1/users/{accessKeyId}`
+
+## Auth Setup
+
+Required when `AUTH_ENABLED=true`:
+- `AUTH_MASTER_KEY` must be base64 for 32 decoded bytes (AES-256 key), e.g. `openssl rand -base64 32`
+- `AUTH_BOOTSTRAP_ACCESS_KEY` and `AUTH_BOOTSTRAP_SECRET_KEY` define initial credentials
+- `ADMIN_API_ENABLED=true` enables `/_admin/v1/*` routes (bootstrap key only)
+
+Reference: `auth/README.md`
+
+Additional docs:
+- Admin OpenAPI spec: `docs/admin-api-openapi.yaml`
+- S3 compatibility matrix: `docs/s3-compatibility.md`
+
 Health:
 - `GET /healthz`
 - `HEAD /healthz`
+- `GET /metrics` (Prometheus exposition format)
+- `HEAD /metrics`
 
 ## Limitations
 
-- No authentication/authorization yet.
 - Not full S3 API coverage.
 - No versioning or lifecycle policies.
 - Error and edge-case behavior is still being refined for client compatibility.

api/admin_api.go

@@ -0,0 +1,300 @@
+package api
+
+import (
+	"encoding/json"
+	"errors"
+	"fs/auth"
+	"fs/models"
+	"io"
+	"net/http"
+	"strconv"
+	"strings"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/go-chi/chi/v5/middleware"
+)
+
+const (
+	maxAdminJSONBodyBytes = 1 << 20
+	defaultAdminPageSize  = 100
+	maxAdminPageSize      = 1000
+)
+
+type adminErrorResponse struct {
+	Code      string `json:"code"`
+	Message   string `json:"message"`
+	RequestID string `json:"requestId,omitempty"`
+}
+
+type adminCreateUserRequest struct {
+	AccessKeyID string            `json:"accessKeyId"`
+	SecretKey   string            `json:"secretKey,omitempty"`
+	Status      string            `json:"status,omitempty"`
+	Policy      models.AuthPolicy `json:"policy"`
+}
+
+type adminSetPolicyRequest struct {
+	Policy models.AuthPolicy `json:"policy"`
+}
+
+type adminSetStatusRequest struct {
+	Status string `json:"status"`
+}
+
+type adminUserListItem struct {
+	AccessKeyID string `json:"accessKeyId"`
+	Status      string `json:"status"`
+	CreatedAt   int64  `json:"createdAt"`
+	UpdatedAt   int64  `json:"updatedAt"`
+}
+
+type adminUserListResponse struct {
+	Items      []adminUserListItem `json:"items"`
+	NextCursor string              `json:"nextCursor,omitempty"`
+}
+
+type adminUserResponse struct {
+	AccessKeyID string             `json:"accessKeyId"`
+	Status      string             `json:"status"`
+	CreatedAt   int64              `json:"createdAt"`
+	UpdatedAt   int64              `json:"updatedAt"`
+	Policy      *models.AuthPolicy `json:"policy,omitempty"`
+	SecretKey   string             `json:"secretKey,omitempty"`
+}
+
+func (h *Handler) registerAdminRoutes() {
+	h.router.Route("/_admin/v1", func(r chi.Router) {
+		r.Post("/users", h.handleAdminCreateUser)
+		r.Get("/users", h.handleAdminListUsers)
+		r.Get("/users/{accessKeyId}", h.handleAdminGetUser)
+		r.Put("/users/{accessKeyId}/policy", h.handleAdminSetUserPolicy)
+		r.Put("/users/{accessKeyId}/status", h.handleAdminSetUserStatus)
+		r.Delete("/users/{accessKeyId}", h.handleAdminDeleteUser)
+	})
+}
+
+func (h *Handler) handleAdminCreateUser(w http.ResponseWriter, r *http.Request) {
+	if !h.requireBootstrapAdmin(w, r) {
+		return
+	}
+
+	var req adminCreateUserRequest
+	if err := decodeJSONBody(w, r, &req); err != nil {
+		writeAdminError(w, r, http.StatusBadRequest, "InvalidRequest", err.Error())
+		return
+	}
+
+	created, err := h.authSvc.CreateUser(auth.CreateUserInput{
+		AccessKeyID: req.AccessKeyID,
+		SecretKey:   req.SecretKey,
+		Status:      req.Status,
+		Policy:      req.Policy,
+	})
+	if err != nil {
+		writeMappedAdminError(w, r, err)
+		return
+	}
+
+	resp := adminUserResponse{
+		AccessKeyID: created.AccessKeyID,
+		Status:      created.Status,
+		CreatedAt:   created.CreatedAt,
+		UpdatedAt:   created.UpdatedAt,
+		Policy:      &created.Policy,
+		SecretKey:   created.SecretKey,
+	}
+	writeJSON(w, http.StatusCreated, resp)
+}
+
+func (h *Handler) handleAdminListUsers(w http.ResponseWriter, r *http.Request) {
+	if !h.requireBootstrapAdmin(w, r) {
+		return
+	}
+
+	limit := defaultAdminPageSize
+	if raw := strings.TrimSpace(r.URL.Query().Get("limit")); raw != "" {
+		parsed, err := strconv.Atoi(raw)
+		if err != nil || parsed < 1 || parsed > maxAdminPageSize {
+			writeAdminError(w, r, http.StatusBadRequest, "InvalidRequest", "limit must be between 1 and 1000")
+			return
+		}
+		limit = parsed
+	}
+	cursor := strings.TrimSpace(r.URL.Query().Get("cursor"))
+
+	users, nextCursor, err := h.authSvc.ListUsers(limit, cursor)
+	if err != nil {
+		writeMappedAdminError(w, r, err)
+		return
+	}
+
+	items := make([]adminUserListItem, 0, len(users))
+	for _, user := range users {
+		items = append(items, adminUserListItem{
+			AccessKeyID: user.AccessKeyID,
+			Status:      user.Status,
+			CreatedAt:   user.CreatedAt,
+			UpdatedAt:   user.UpdatedAt,
+		})
+	}
+
+	writeJSON(w, http.StatusOK, adminUserListResponse{
+		Items:      items,
+		NextCursor: nextCursor,
+	})
+}
+
+func (h *Handler) handleAdminGetUser(w http.ResponseWriter, r *http.Request) {
+	if !h.requireBootstrapAdmin(w, r) {
+		return
+	}
+
+	accessKeyID := chi.URLParam(r, "accessKeyId")
+	user, err := h.authSvc.GetUser(accessKeyID)
+	if err != nil {
+		writeMappedAdminError(w, r, err)
+		return
+	}
+
+	resp := adminUserResponse{
+		AccessKeyID: user.AccessKeyID,
+		Status:      user.Status,
+		CreatedAt:   user.CreatedAt,
+		UpdatedAt:   user.UpdatedAt,
+		Policy:      &user.Policy,
+	}
+	writeJSON(w, http.StatusOK, resp)
+}
+
+func (h *Handler) handleAdminDeleteUser(w http.ResponseWriter, r *http.Request) {
+	if !h.requireBootstrapAdmin(w, r) {
+		return
+	}
+	accessKeyID := chi.URLParam(r, "accessKeyId")
+	if err := h.authSvc.DeleteUser(accessKeyID); err != nil {
+		writeMappedAdminError(w, r, err)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}
+
+func (h *Handler) handleAdminSetUserPolicy(w http.ResponseWriter, r *http.Request) {
+	if !h.requireBootstrapAdmin(w, r) {
+		return
+	}
+
+	accessKeyID := chi.URLParam(r, "accessKeyId")
+	var req adminSetPolicyRequest
+	if err := decodeJSONBody(w, r, &req); err != nil {
+		writeAdminError(w, r, http.StatusBadRequest, "InvalidRequest", err.Error())
+		return
+	}
+
+	user, err := h.authSvc.SetUserPolicy(accessKeyID, req.Policy)
+	if err != nil {
+		writeMappedAdminError(w, r, err)
+		return
+	}
+	resp := adminUserResponse{
+		AccessKeyID: user.AccessKeyID,
+		Status:      user.Status,
+		CreatedAt:   user.CreatedAt,
+		UpdatedAt:   user.UpdatedAt,
+		Policy:      &user.Policy,
+	}
+	writeJSON(w, http.StatusOK, resp)
+}
+
+func (h *Handler) handleAdminSetUserStatus(w http.ResponseWriter, r *http.Request) {
+	if !h.requireBootstrapAdmin(w, r) {
+		return
+	}
+
+	accessKeyID := chi.URLParam(r, "accessKeyId")
+	var req adminSetStatusRequest
+	if err := decodeJSONBody(w, r, &req); err != nil {
+		writeAdminError(w, r, http.StatusBadRequest, "InvalidRequest", err.Error())
+		return
+	}
+
+	user, err := h.authSvc.SetUserStatus(accessKeyID, req.Status)
+	if err != nil {
+		writeMappedAdminError(w, r, err)
+		return
+	}
+	resp := adminUserResponse{
+		AccessKeyID: user.AccessKeyID,
+		Status:      user.Status,
+		CreatedAt:   user.CreatedAt,
+		UpdatedAt:   user.UpdatedAt,
+		Policy:      &user.Policy,
+	}
+	writeJSON(w, http.StatusOK, resp)
+}
+
+func (h *Handler) requireBootstrapAdmin(w http.ResponseWriter, r *http.Request) bool {
+	authCtx, ok := auth.GetRequestContext(r.Context())
+	if !ok || !authCtx.Authenticated {
+		writeAdminError(w, r, http.StatusForbidden, "Forbidden", "admin credentials are required")
+		return false
+	}
+	if h.authSvc == nil {
+		writeAdminError(w, r, http.StatusForbidden, "Forbidden", "admin access is not configured")
+		return false
+	}
+
+	bootstrap := strings.TrimSpace(h.authSvc.Config().BootstrapAccessKey)
+	if bootstrap == "" || authCtx.AccessKeyID != bootstrap {
+		writeAdminError(w, r, http.StatusForbidden, "Forbidden", "admin access denied")
+		return false
+	}
+	return true
+}
+
+func decodeJSONBody(w http.ResponseWriter, r *http.Request, dst any) error {
+	r.Body = http.MaxBytesReader(w, r.Body, maxAdminJSONBodyBytes)
+	decoder := json.NewDecoder(r.Body)
+	decoder.DisallowUnknownFields()
+	if err := decoder.Decode(dst); err != nil {
+		return err
+	}
+	if err := decoder.Decode(&struct{}{}); err != io.EOF {
+		return errors.New("request body must contain a single JSON object")
+	}
+	return nil
+}
+
+func writeMappedAdminError(w http.ResponseWriter, r *http.Request, err error) {
+	switch {
+	case errors.Is(err, auth.ErrInvalidUserInput):
+		writeAdminError(w, r, http.StatusBadRequest, "InvalidRequest", err.Error())
+	case errors.Is(err, auth.ErrUserAlreadyExists):
+		writeAdminError(w, r, http.StatusConflict, "UserAlreadyExists", "user already exists")
+	case errors.Is(err, auth.ErrUserNotFound):
+		writeAdminError(w, r, http.StatusNotFound, "UserNotFound", "user was not found")
+	case errors.Is(err, auth.ErrAuthNotEnabled):
+		writeAdminError(w, r, http.StatusServiceUnavailable, "AuthDisabled", "authentication subsystem is disabled")
+	default:
+		writeAdminError(w, r, http.StatusInternalServerError, "InternalError", "internal server error")
+	}
+}
+
+func writeAdminError(w http.ResponseWriter, r *http.Request, status int, code string, message string) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	requestID := middleware.GetReqID(r.Context())
+	if requestID != "" {
+		w.Header().Set("x-amz-request-id", requestID)
+	}
+	w.WriteHeader(status)
+	_ = json.NewEncoder(w).Encode(adminErrorResponse{
+		Code:      code,
+		Message:   message,
+		RequestID: requestID,
+	})
+}
+
+func writeJSON(w http.ResponseWriter, status int, payload any) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	w.WriteHeader(status)
+	_ = json.NewEncoder(w).Encode(payload)
+}

api/api.go

@@ -7,8 +7,10 @@ import (
 	"encoding/xml"
 	"errors"
 	"fmt"
+	"fs/auth"
 	"fs/logging"
 	"fs/metadata"
+	"fs/metrics"
 	"fs/models"
 	"fs/service"
 	"io"
@@ -30,6 +32,8 @@ type Handler struct {
 	svc       *service.ObjectService
 	logger    *slog.Logger
 	logConfig logging.Config
+	authSvc   *auth.Service
+	adminAPI  bool
 }
 
 const (
@@ -44,7 +48,7 @@ const (
 	serverMaxConnections          = 1024
 )
 
-func NewHandler(svc *service.ObjectService, logger *slog.Logger, logConfig logging.Config) *Handler {
+func NewHandler(svc *service.ObjectService, logger *slog.Logger, logConfig logging.Config, authSvc *auth.Service, adminAPI bool) *Handler {
 	r := chi.NewRouter()
 	r.Use(middleware.RequestID)
 	r.Use(middleware.Recoverer)
@@ -57,16 +61,24 @@ func NewHandler(svc *service.ObjectService, logger *slog.Logger, logConfig loggi
 		svc:       svc,
 		logger:    logger,
 		logConfig: logConfig,
+		authSvc:   authSvc,
+		adminAPI:  adminAPI,
 	}
 	return h
 }
 
 func (h *Handler) setupRoutes() {
 	h.router.Use(logging.HTTPMiddleware(h.logger, h.logConfig))
+	h.router.Use(auth.Middleware(h.authSvc, h.logger, h.logConfig.Audit, writeMappedS3Error))
 
 	h.router.Get("/healthz", h.handleHealth)
 	h.router.Head("/healthz", h.handleHealth)
+	h.router.Get("/metrics", h.handleMetrics)
+	h.router.Head("/metrics", h.handleMetrics)
 	h.router.Get("/", h.handleGetBuckets)
+	if h.adminAPI {
+		h.registerAdminRoutes()
+	}
 
 	h.router.Get("/{bucket}/", h.handleGetBucket)
 	h.router.Get("/{bucket}", h.handleGetBucket)
@@ -102,6 +114,18 @@ func (h *Handler) handleHealth(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func (h *Handler) handleMetrics(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "text/plain; version=0.0.4; charset=utf-8")
+	if r.Method == http.MethodHead {
+		w.WriteHeader(http.StatusOK)
+		return
+	}
+	payload := metrics.Default.RenderPrometheus()
+	w.Header().Set("Content-Length", strconv.Itoa(len(payload)))
+	w.WriteHeader(http.StatusOK)
+	_, _ = w.Write([]byte(payload))
+}
+
 func validateObjectKey(key string) *s3APIError {
 	if key == "" {
 		err := s3ErrInvalidObjectKey
@@ -218,6 +242,7 @@ func (h *Handler) handlePostObject(w http.ResponseWriter, r *http.Request) {
 			writeS3Error(w, r, s3ErrMalformedXML, r.URL.Path)
 			return
 		}
+		metrics.Default.ObserveBatchSize(len(req.Parts))
 
 		manifest, err := h.svc.CompleteMultipartUpload(bucket, key, uploadID, req.Parts)
 		if err != nil {
@@ -293,6 +318,20 @@ func (h *Handler) handlePutObject(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusOK)
 		return
 	}
+	metrics.Default.ObserveBatchSize(1)
+
+	if ifNoneMatch := strings.TrimSpace(r.Header.Get("If-None-Match")); ifNoneMatch != "" {
+		manifest, err := h.svc.HeadObject(bucket, key)
+		if err != nil {
+			if !errors.Is(err, metadata.ErrObjectNotFound) {
+				writeMappedS3Error(w, r, err)
+				return
+			}
+		} else if ifNoneMatchPreconditionFailed(ifNoneMatch, manifest.ETag) {
+			writeS3Error(w, r, s3ErrPreconditionFailed, r.URL.Path)
+			return
+		}
+	}
 
 	contentType := r.Header.Get("Content-Type")
 	if contentType == "" {
@@ -424,6 +463,25 @@ func decodeAWSChunkedPayload(src io.Reader, dst io.Writer) error {
 	}
 }
 
+func ifNoneMatchPreconditionFailed(headerValue, etag string) bool {
+	for _, rawToken := range strings.Split(headerValue, ",") {
+		token := strings.TrimSpace(rawToken)
+		if token == "" {
+			continue
+		}
+		if token == "*" {
+			return true
+		}
+
+		token = strings.TrimPrefix(token, "W/")
+		token = strings.Trim(token, `"`)
+		if strings.EqualFold(token, etag) {
+			return true
+		}
+	}
+	return false
+}
+
 func (h *Handler) handlePutBucket(w http.ResponseWriter, r *http.Request) {
 	bucket := chi.URLParam(r, "bucket")
 	if err := h.svc.CreateBucket(bucket); err != nil {
@@ -473,6 +531,7 @@ func (h *Handler) handlePostBucket(w http.ResponseWriter, r *http.Request) {
 		writeS3Error(w, r, s3ErrTooManyDeleteObjects, r.URL.Path)
 		return
 	}
+	metrics.Default.ObserveBatchSize(len(req.Objects))
 
 	keys := make([]string, 0, len(req.Objects))
 	response := models.DeleteObjectsResult{
@@ -591,6 +650,7 @@ func newLimitedListener(inner net.Listener, maxConns int) net.Listener {
 	if maxConns <= 0 {
 		return inner
 	}
+	metrics.Default.SetConnectionPoolMax(maxConns)
 	return &limitedListener{
 		Listener: inner,
 		slots:    make(chan struct{}, maxConns),
@@ -598,15 +658,26 @@ func newLimitedListener(inner net.Listener, maxConns int) net.Listener {
 }
 
 func (l *limitedListener) Accept() (net.Conn, error) {
-	l.slots <- struct{}{}
+	select {
+	case l.slots <- struct{}{}:
+	default:
+		metrics.Default.IncConnectionPoolWait()
+		metrics.Default.IncRequestQueueLength()
+		l.slots <- struct{}{}
+		metrics.Default.DecRequestQueueLength()
+	}
 	conn, err := l.Listener.Accept()
 	if err != nil {
 		<-l.slots
 		return nil, err
 	}
+	metrics.Default.IncConnectionPoolActive()
 	return &limitedConn{
 		Conn: conn,
-		done: func() { <-l.slots },
+		done: func() {
+			<-l.slots
+			metrics.Default.DecConnectionPoolActive()
+		},
 	}, nil
 }
 
@@ -666,26 +737,203 @@ func (h *Handler) handleGetBuckets(w http.ResponseWriter, r *http.Request) {
 
 func (h *Handler) handleGetBucket(w http.ResponseWriter, r *http.Request) {
 	bucket := chi.URLParam(r, "bucket")
+	query := r.URL.Query()
 
-	if r.URL.Query().Get("list-type") == "2" {
-		h.handleListObjectsV2(w, r, bucket)
-		return
-	}
-	if r.URL.Query().Has("location") {
-		xmlResponse := `<?xml version="1.0" encoding="UTF-8"?>
-						<LocationConstraint xmlns="http://s3.amazonaws.com/doc/2006-03-01/">us-east-1</LocationConstraint>`
+	if query.Has("location") {
+		region := "us-east-1"
+		if h.authSvc != nil {
+			candidate := strings.TrimSpace(h.authSvc.Config().Region)
+			if candidate != "" {
+				region = candidate
+			}
+		}
+		xmlResponse := fmt.Sprintf(`<?xml version="1.0" encoding="UTF-8"?>
+<LocationConstraint xmlns="http://s3.amazonaws.com/doc/2006-03-01/">%s</LocationConstraint>`, region)
 
 		w.Header().Set("Content-Type", "application/xml; charset=utf-8")
 		w.Header().Set("Content-Length", strconv.Itoa(len(xmlResponse)))
 		w.WriteHeader(http.StatusOK)
-		_, err := w.Write([]byte(xmlResponse))
-		if err != nil {
-			return
-		}
+		_, _ = w.Write([]byte(xmlResponse))
 		return
 	}
-	writeS3Error(w, r, s3ErrNotImplemented, r.URL.Path)
 
+	listType := strings.TrimSpace(query.Get("list-type"))
+	if listType == "2" {
+		h.handleListObjectsV2(w, r, bucket)
+		return
+	}
+	if listType != "" {
+		writeS3Error(w, r, s3ErrInvalidArgument, r.URL.Path)
+		return
+	}
+
+	if shouldUseListObjectsV1(query) {
+		h.handleListObjectsV1(w, r, bucket)
+		return
+	}
+
+	writeS3Error(w, r, s3ErrNotImplemented, r.URL.Path)
+}
+
+func shouldUseListObjectsV1(query url.Values) bool {
+	if len(query) == 0 {
+		return true
+	}
+
+	listingParams := map[string]struct{}{
+		"delimiter":     {},
+		"encoding-type": {},
+		"marker":        {},
+		"max-keys":      {},
+		"prefix":        {},
+	}
+	for key := range query {
+		if _, ok := listingParams[key]; !ok {
+			return false
+		}
+	}
+	return true
+}
+
+func (h *Handler) handleListObjectsV1(w http.ResponseWriter, r *http.Request, bucket string) {
+	prefix := r.URL.Query().Get("prefix")
+	delimiter := r.URL.Query().Get("delimiter")
+	marker := r.URL.Query().Get("marker")
+	encodingType := strings.ToLower(strings.TrimSpace(r.URL.Query().Get("encoding-type")))
+	if encodingType != "" && encodingType != "url" {
+		writeS3Error(w, r, s3ErrInvalidArgument, r.URL.Path)
+		return
+	}
+
+	maxKeys := 1000
+	if rawMaxKeys := strings.TrimSpace(r.URL.Query().Get("max-keys")); rawMaxKeys != "" {
+		parsed, err := strconv.Atoi(rawMaxKeys)
+		if err != nil || parsed < 0 {
+			writeS3Error(w, r, s3ErrInvalidArgument, r.URL.Path)
+			return
+		}
+		if parsed > 1000 {
+			parsed = 1000
+		}
+		maxKeys = parsed
+	}
+
+	result := models.ListBucketResultV1{
+		Xmlns:        "http://s3.amazonaws.com/doc/2006-03-01/",
+		Name:         bucket,
+		Prefix:       s3EncodeIfNeeded(prefix, encodingType),
+		Marker:       s3EncodeIfNeeded(marker, encodingType),
+		Delimiter:    s3EncodeIfNeeded(delimiter, encodingType),
+		MaxKeys:      maxKeys,
+		EncodingType: encodingType,
+	}
+
+	type pageEntry struct {
+		Object       *models.ObjectManifest
+		CommonPrefix string
+	}
+
+	entries := make([]pageEntry, 0, maxKeys)
+	seenCommonPrefixes := make(map[string]struct{})
+	truncated := false
+	stopErr := errors.New("list_v1_page_complete")
+
+	startKey := prefix
+	if marker != "" && marker > startKey {
+		startKey = marker
+	}
+
+	if maxKeys > 0 {
+		err := h.svc.ForEachObjectFrom(bucket, startKey, func(object *models.ObjectManifest) error {
+			if object == nil {
+				return nil
+			}
+			key := object.Key
+
+			if prefix != "" {
+				if key < prefix {
+					return nil
+				}
+				if !strings.HasPrefix(key, prefix) {
+					return stopErr
+				}
+			}
+			if marker != "" && key <= marker {
+				return nil
+			}
+
+			if delimiter != "" {
+				relative := strings.TrimPrefix(key, prefix)
+				if idx := strings.Index(relative, delimiter); idx >= 0 {
+					commonPrefix := prefix + relative[:idx+len(delimiter)]
+					if marker != "" && commonPrefix <= marker {
+						return nil
+					}
+					if _, exists := seenCommonPrefixes[commonPrefix]; exists {
+						return nil
+					}
+					seenCommonPrefixes[commonPrefix] = struct{}{}
+					if len(entries) >= maxKeys {
+						truncated = true
+						return stopErr
+					}
+					entries = append(entries, pageEntry{
+						CommonPrefix: commonPrefix,
+					})
+					return nil
+				}
+			}
+
+			if len(entries) >= maxKeys {
+				truncated = true
+				return stopErr
+			}
+			entries = append(entries, pageEntry{Object: object})
+			return nil
+		})
+		if err != nil && !errors.Is(err, stopErr) {
+			writeMappedS3Error(w, r, err)
+			return
+		}
+	}
+
+	for _, entry := range entries {
+		if entry.Object != nil {
+			result.Contents = append(result.Contents, models.Contents{
+				Key:          s3EncodeIfNeeded(entry.Object.Key, encodingType),
+				LastModified: time.Unix(entry.Object.CreatedAt, 0).UTC().Format("2006-01-02T15:04:05.000Z"),
+				ETag:         `"` + entry.Object.ETag + `"`,
+				Size:         entry.Object.Size,
+				StorageClass: "STANDARD",
+			})
+		} else {
+			result.CommonPrefixes = append(result.CommonPrefixes, models.CommonPrefixes{
+				Prefix: s3EncodeIfNeeded(entry.CommonPrefix, encodingType),
+			})
+		}
+	}
+
+	result.IsTruncated = truncated
+	if result.IsTruncated && result.NextMarker == "" && len(entries) > 0 {
+		last := entries[len(entries)-1]
+		if last.Object != nil {
+			result.NextMarker = s3EncodeIfNeeded(last.Object.Key, encodingType)
+		} else {
+			result.NextMarker = s3EncodeIfNeeded(last.CommonPrefix, encodingType)
+		}
+	}
+
+	xmlResponse, err := xml.MarshalIndent(result, "", "    ")
+	if err != nil {
+		writeMappedS3Error(w, r, err)
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/xml; charset=utf-8")
+	w.Header().Set("Content-Length", strconv.Itoa(len(xml.Header)+len(xmlResponse)))
+	w.WriteHeader(http.StatusOK)
+	_, _ = w.Write([]byte(xml.Header))
+	_, _ = w.Write(xmlResponse)
 }
 
 func (h *Handler) handleListObjectsV2(w http.ResponseWriter, r *http.Request, bucket string) {

api/s3_errors.go

@@ -3,7 +3,9 @@ package api
 import (
 	"encoding/xml"
 	"errors"
+	"fs/auth"
 	"fs/metadata"
+	"fs/metrics"
 	"fs/models"
 	"fs/service"
 	"net/http"
@@ -58,6 +60,11 @@ var (
 		Code:    "InvalidRange",
 		Message: "The requested range is not satisfiable.",
 	}
+	s3ErrPreconditionFailed = s3APIError{
+		Status:  http.StatusPreconditionFailed,
+		Code:    "PreconditionFailed",
+		Message: "At least one of the pre-conditions you specified did not hold.",
+	}
 	s3ErrEntityTooSmall = s3APIError{
 		Status:  http.StatusBadRequest,
 		Code:    "EntityTooSmall",
@@ -73,6 +80,41 @@ var (
 		Code:    "MalformedXML",
 		Message: "The request must contain no more than 1000 object identifiers.",
 	}
+	s3ErrAccessDenied = s3APIError{
+		Status:  http.StatusForbidden,
+		Code:    "AccessDenied",
+		Message: "Access Denied.",
+	}
+	s3ErrInvalidAccessKeyID = s3APIError{
+		Status:  http.StatusForbidden,
+		Code:    "InvalidAccessKeyId",
+		Message: "The AWS Access Key Id you provided does not exist in our records.",
+	}
+	s3ErrSignatureDoesNotMatch = s3APIError{
+		Status:  http.StatusForbidden,
+		Code:    "SignatureDoesNotMatch",
+		Message: "The request signature we calculated does not match the signature you provided.",
+	}
+	s3ErrAuthorizationHeaderMalformed = s3APIError{
+		Status:  http.StatusBadRequest,
+		Code:    "AuthorizationHeaderMalformed",
+		Message: "The authorization header is malformed; the region/service/date is wrong or missing.",
+	}
+	s3ErrRequestTimeTooSkewed = s3APIError{
+		Status:  http.StatusForbidden,
+		Code:    "RequestTimeTooSkewed",
+		Message: "The difference between the request time and the server's time is too large.",
+	}
+	s3ErrExpiredToken = s3APIError{
+		Status:  http.StatusBadRequest,
+		Code:    "ExpiredToken",
+		Message: "The provided token has expired.",
+	}
+	s3ErrInvalidPresign = s3APIError{
+		Status:  http.StatusBadRequest,
+		Code:    "AuthorizationQueryParametersError",
+		Message: "Error parsing the X-Amz-Credential parameter.",
+	}
 	s3ErrInternal = s3APIError{
 		Status:  http.StatusInternalServerError,
 		Code:    "InternalError",
@@ -132,6 +174,26 @@ func mapToS3Error(err error) s3APIError {
 		return s3ErrMalformedXML
 	case errors.Is(err, service.ErrEntityTooSmall):
 		return s3ErrEntityTooSmall
+	case errors.Is(err, auth.ErrAccessDenied):
+		return s3ErrAccessDenied
+	case errors.Is(err, auth.ErrInvalidAccessKeyID):
+		return s3ErrInvalidAccessKeyID
+	case errors.Is(err, auth.ErrSignatureDoesNotMatch):
+		return s3ErrSignatureDoesNotMatch
+	case errors.Is(err, auth.ErrAuthorizationHeaderMalformed):
+		return s3ErrAuthorizationHeaderMalformed
+	case errors.Is(err, auth.ErrRequestTimeTooSkewed):
+		return s3ErrRequestTimeTooSkewed
+	case errors.Is(err, auth.ErrExpiredToken):
+		return s3ErrExpiredToken
+	case errors.Is(err, auth.ErrCredentialDisabled):
+		return s3ErrAccessDenied
+	case errors.Is(err, auth.ErrNoAuthCredentials):
+		return s3ErrAccessDenied
+	case errors.Is(err, auth.ErrUnsupportedAuthScheme):
+		return s3ErrAuthorizationHeaderMalformed
+	case errors.Is(err, auth.ErrInvalidPresign):
+		return s3ErrInvalidPresign
 	default:
 		return s3ErrInternal
 	}
@@ -139,12 +201,19 @@ func mapToS3Error(err error) s3APIError {
 
 func writeS3Error(w http.ResponseWriter, r *http.Request, apiErr s3APIError, resource string) {
 	requestID := ""
+	op := "other"
 	if r != nil {
 		requestID = middleware.GetReqID(r.Context())
+		isDeletePost := false
+		if r.Method == http.MethodPost {
+			_, isDeletePost = r.URL.Query()["delete"]
+		}
+		op = metrics.NormalizeHTTPOperation(r.Method, isDeletePost)
 		if requestID != "" {
 			w.Header().Set("x-amz-request-id", requestID)
 		}
 	}
+	metrics.Default.ObserveError(op, apiErr.Code)
 	w.Header().Set("Content-Type", "application/xml; charset=utf-8")
 	w.WriteHeader(apiErr.Status)
 

auth/README.md

@@ -0,0 +1,150 @@
+# Authentication Design
+
+This folder implements S3-compatible request authentication using AWS Signature Version 4 (SigV4), with local identity and policy data stored in bbolt.
+
+## Goals
+- Keep S3 client compatibility for request signing.
+- Avoid external auth databases.
+- Store secrets encrypted at rest (not plaintext in bbolt).
+- Keep authorization simple and explicit.
+
+## High-Level Architecture
+- `auth/middleware.go`
+  - HTTP middleware that enforces auth before API handlers.
+  - Exempts `/healthz`.
+  - Calls auth service and writes mapped S3 XML errors on failure.
+- `auth/service.go`
+  - Main auth orchestration:
+    - parse SigV4 from request
+    - validate timestamp/scope/service/region
+    - load identity from metadata
+    - decrypt secret
+    - verify signature
+    - evaluate policy against requested S3 action
+- `auth/sigv4.go`
+  - Canonical SigV4 parsing and verification helpers.
+  - Supports header auth and presigned query auth.
+- `auth/policy.go`
+  - Authorization evaluator (deny overrides allow).
+- `auth/action.go`
+  - Maps HTTP method/path/query to logical S3 action + resource target.
+- `auth/crypto.go`
+  - AES-256-GCM encryption/decryption for stored secret keys.
+- `auth/context.go`
+  - Carries authentication result in request context for downstream logic.
+- `auth/config.go`
+  - Normalized auth configuration.
+- `auth/errors.go`
+  - Domain auth errors used by API S3 error mapping.
+
+## Config Model
+Auth is configured through env (read in `utils/config.go`, converted in `auth/config.go`):
+
+- `AUTH_ENABLED`
+- `AUTH_REGION`
+- `AUTH_SKEW_SECONDS`
+- `AUTH_MAX_PRESIGN_SECONDS`
+- `AUTH_MASTER_KEY`
+- `AUTH_BOOTSTRAP_ACCESS_KEY`
+- `AUTH_BOOTSTRAP_SECRET_KEY`
+- `AUTH_BOOTSTRAP_POLICY` (optional JSON)
+
+Important:
+- If `AUTH_ENABLED=true`, `AUTH_MASTER_KEY` is required.
+- `AUTH_MASTER_KEY` must be base64 that decodes to exactly 32 bytes (AES-256 key).
+
+## Persistence Model (bbolt)
+Implemented in metadata layer:
+- `__AUTH_IDENTITIES__` bucket stores `models.AuthIdentity`
+  - `access_key_id`
+  - encrypted secret (`secret_enc`, `secret_nonce`)
+  - status (`active`/disabled)
+  - timestamps
+- `__AUTH_POLICIES__` bucket stores `models.AuthPolicy`
+  - `principal`
+  - statements (`effect`, `actions`, `bucket`, `prefix`)
+
+## Bootstrap Identity
+On startup (`main.go`):
+1. Build auth config.
+2. Create auth service with metadata store.
+3. Call `EnsureBootstrap()`.
+
+If bootstrap env key/secret are set:
+- identity is created/updated
+- secret is encrypted with AES-GCM and stored
+- policy is created:
+  - default: full access (`s3:*`, `bucket=*`, `prefix=*`)
+  - or overridden by `AUTH_BOOTSTRAP_POLICY`
+
+## Request Authentication Flow
+For each non-health request:
+1. Parse SigV4 input (header or presigned query).
+2. Validate structural fields:
+  - algorithm
+  - credential scope
+  - service must be `s3`
+  - region must match config
+3. Validate time:
+  - `x-amz-date` format
+  - skew within `AUTH_SKEW_SECONDS`
+  - presigned expiry within `AUTH_MAX_PRESIGN_SECONDS`
+4. Load identity by access key id.
+5. Ensure identity status is active.
+6. Decrypt stored secret using master key.
+7. Recompute canonical request and expected signature.
+8. Compare signatures.
+9. Resolve target action from request.
+10. Evaluate policy; deny overrides allow.
+11. Store auth result in request context and continue.
+
+## Authorization Semantics
+Policy evaluator rules:
+- No matching allow => denied.
+- Any matching deny => denied (even if allow also matches).
+- Wildcards supported:
+  - action: `*` or `s3:*`
+  - bucket: `*`
+  - prefix: `*`
+
+Action resolution includes:
+- bucket APIs (`CreateBucket`, `ListBucket`, `HeadBucket`, `DeleteBucket`)
+- object APIs (`GetObject`, `PutObject`, `DeleteObject`)
+- multipart APIs (`CreateMultipartUpload`, `UploadPart`, `ListMultipartUploadParts`, `CompleteMultipartUpload`, `AbortMultipartUpload`)
+
+## Error Behavior
+Auth errors are mapped to S3-style XML errors in `api/s3_errors.go`, including:
+- `AccessDenied`
+- `InvalidAccessKeyId`
+- `SignatureDoesNotMatch`
+- `AuthorizationHeaderMalformed`
+- `RequestTimeTooSkewed`
+- `ExpiredToken`
+- `AuthorizationQueryParametersError`
+
+## Audit Logging
+When `AUDIT_LOG=true` and auth is enabled:
+- successful auth attempts emit `auth_success`
+- failed auth attempts emit `auth_failed`
+
+Each audit entry includes method, path, remote IP, and request ID (if present). Success logs also include access key ID and auth type.
+
+## Security Notes
+- Secret keys are recoverable by server design (required for SigV4 verification).
+- They are encrypted at rest, not hashed.
+- Master key rotation is not implemented yet.
+- Keep `AUTH_MASTER_KEY` protected (secret manager/systemd env file/etc.).
+
+## Current Scope / Limitations
+- No STS/session-token auth yet.
+- No admin API for managing multiple users yet.
+- Policy language is intentionally minimal, not full IAM.
+- No automatic key rotation workflows.
+
+## Practical Next Step
+To support multiple users cleanly, add admin operations in auth service + API:
+- create user
+- rotate secret
+- set policy
+- disable/enable
+- delete user

auth/action.go

@@ -0,0 +1,93 @@
+package auth
+
+import (
+	"net/http"
+	"strings"
+)
+
+type Action string
+
+const (
+	ActionListAllMyBuckets      Action = "s3:ListAllMyBuckets"
+	ActionCreateBucket          Action = "s3:CreateBucket"
+	ActionHeadBucket            Action = "s3:HeadBucket"
+	ActionDeleteBucket          Action = "s3:DeleteBucket"
+	ActionListBucket            Action = "s3:ListBucket"
+	ActionGetObject             Action = "s3:GetObject"
+	ActionPutObject             Action = "s3:PutObject"
+	ActionDeleteObject          Action = "s3:DeleteObject"
+	ActionCreateMultipartUpload Action = "s3:CreateMultipartUpload"
+	ActionUploadPart            Action = "s3:UploadPart"
+	ActionListMultipartParts    Action = "s3:ListMultipartUploadParts"
+	ActionCompleteMultipart     Action = "s3:CompleteMultipartUpload"
+	ActionAbortMultipartUpload  Action = "s3:AbortMultipartUpload"
+)
+
+type RequestTarget struct {
+	Action Action
+	Bucket string
+	Key    string
+}
+
+func resolveTarget(r *http.Request) RequestTarget {
+	path := strings.TrimPrefix(r.URL.Path, "/")
+	if path == "" {
+		return RequestTarget{Action: ActionListAllMyBuckets}
+	}
+
+	parts := strings.SplitN(path, "/", 2)
+	bucket := parts[0]
+	key := ""
+	if len(parts) > 1 {
+		key = parts[1]
+	}
+
+	if key == "" {
+		switch r.Method {
+		case http.MethodPut:
+			return RequestTarget{Action: ActionCreateBucket, Bucket: bucket}
+		case http.MethodHead:
+			return RequestTarget{Action: ActionHeadBucket, Bucket: bucket}
+		case http.MethodDelete:
+			return RequestTarget{Action: ActionDeleteBucket, Bucket: bucket}
+		case http.MethodGet:
+			return RequestTarget{Action: ActionListBucket, Bucket: bucket}
+		case http.MethodPost:
+			if _, ok := r.URL.Query()["delete"]; ok {
+				return RequestTarget{Action: ActionDeleteObject, Bucket: bucket}
+			}
+		}
+		return RequestTarget{Bucket: bucket}
+	}
+
+	uploadID := r.URL.Query().Get("uploadId")
+	partNumber := r.URL.Query().Get("partNumber")
+	if _, ok := r.URL.Query()["uploads"]; ok && r.Method == http.MethodPost {
+		return RequestTarget{Action: ActionCreateMultipartUpload, Bucket: bucket, Key: key}
+	}
+	if uploadID != "" {
+		switch r.Method {
+		case http.MethodPut:
+			if partNumber != "" {
+				return RequestTarget{Action: ActionUploadPart, Bucket: bucket, Key: key}
+			}
+		case http.MethodGet:
+			return RequestTarget{Action: ActionListMultipartParts, Bucket: bucket, Key: key}
+		case http.MethodPost:
+			return RequestTarget{Action: ActionCompleteMultipart, Bucket: bucket, Key: key}
+		case http.MethodDelete:
+			return RequestTarget{Action: ActionAbortMultipartUpload, Bucket: bucket, Key: key}
+		}
+	}
+
+	switch r.Method {
+	case http.MethodGet, http.MethodHead:
+		return RequestTarget{Action: ActionGetObject, Bucket: bucket, Key: key}
+	case http.MethodPut:
+		return RequestTarget{Action: ActionPutObject, Bucket: bucket, Key: key}
+	case http.MethodDelete:
+		return RequestTarget{Action: ActionDeleteObject, Bucket: bucket, Key: key}
+	}
+
+	return RequestTarget{Bucket: bucket, Key: key}
+}

auth/config.go

@@ -0,0 +1,50 @@
+package auth
+
+import (
+	"strings"
+	"time"
+)
+
+type Config struct {
+	Enabled            bool
+	Region             string
+	ClockSkew          time.Duration
+	MaxPresignDuration time.Duration
+	MasterKey          string
+	BootstrapAccessKey string
+	BootstrapSecretKey string
+	BootstrapPolicy    string
+}
+
+func ConfigFromValues(
+	enabled bool,
+	region string,
+	skew time.Duration,
+	maxPresign time.Duration,
+	masterKey string,
+	bootstrapAccessKey string,
+	bootstrapSecretKey string,
+	bootstrapPolicy string,
+) Config {
+	region = strings.TrimSpace(region)
+	if region == "" {
+		region = "us-east-1"
+	}
+	if skew <= 0 {
+		skew = 5 * time.Minute
+	}
+	if maxPresign <= 0 {
+		maxPresign = 24 * time.Hour
+	}
+
+	return Config{
+		Enabled:            enabled,
+		Region:             region,
+		ClockSkew:          skew,
+		MaxPresignDuration: maxPresign,
+		MasterKey:          strings.TrimSpace(masterKey),
+		BootstrapAccessKey: strings.TrimSpace(bootstrapAccessKey),
+		BootstrapSecretKey: strings.TrimSpace(bootstrapSecretKey),
+		BootstrapPolicy:    strings.TrimSpace(bootstrapPolicy),
+	}
+}

auth/context.go

@@ -0,0 +1,23 @@
+package auth
+
+import "context"
+
+type RequestContext struct {
+	Authenticated bool
+	AccessKeyID   string
+	AuthType      string
+}
+
+type contextKey int
+
+const requestContextKey contextKey = iota
+
+func WithRequestContext(ctx context.Context, authCtx RequestContext) context.Context {
+	return context.WithValue(ctx, requestContextKey, authCtx)
+}
+
+func GetRequestContext(ctx context.Context) (RequestContext, bool) {
+	value := ctx.Value(requestContextKey)
+	authCtx, ok := value.(RequestContext)
+	return authCtx, ok
+}

auth/crypto.go

@@ -0,0 +1,74 @@
+package auth
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+	"io"
+)
+
+const (
+	masterKeyLength = 32
+	gcmNonceLength  = 12
+)
+
+func decodeMasterKey(raw string) ([]byte, error) {
+	decoded, err := base64.StdEncoding.DecodeString(raw)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %v", ErrInvalidMasterKey, err)
+	}
+	if len(decoded) != masterKeyLength {
+		return nil, fmt.Errorf("%w: expected %d-byte decoded key", ErrInvalidMasterKey, masterKeyLength)
+	}
+	return decoded, nil
+}
+
+func encryptSecret(masterKey []byte, accessKeyID, secret string) (ciphertextB64 string, nonceB64 string, err error) {
+	block, err := aes.NewCipher(masterKey)
+	if err != nil {
+		return "", "", err
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", "", err
+	}
+
+	nonce := make([]byte, gcmNonceLength)
+	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
+		return "", "", err
+	}
+
+	ciphertext := gcm.Seal(nil, nonce, []byte(secret), []byte(accessKeyID))
+	return base64.StdEncoding.EncodeToString(ciphertext), base64.StdEncoding.EncodeToString(nonce), nil
+}
+
+func decryptSecret(masterKey []byte, accessKeyID, ciphertextB64, nonceB64 string) (string, error) {
+	block, err := aes.NewCipher(masterKey)
+	if err != nil {
+		return "", err
+	}
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+
+	ciphertext, err := base64.StdEncoding.DecodeString(ciphertextB64)
+	if err != nil {
+		return "", err
+	}
+	nonce, err := base64.StdEncoding.DecodeString(nonceB64)
+	if err != nil {
+		return "", err
+	}
+	if len(nonce) != gcmNonceLength {
+		return "", fmt.Errorf("invalid nonce length: %d", len(nonce))
+	}
+
+	plaintext, err := gcm.Open(nil, nonce, ciphertext, []byte(accessKeyID))
+	if err != nil {
+		return "", err
+	}
+	return string(plaintext), nil
+}

auth/errors.go

@@ -0,0 +1,22 @@
+package auth
+
+import "errors"
+
+var (
+	ErrAccessDenied                 = errors.New("access denied")
+	ErrInvalidAccessKeyID           = errors.New("invalid access key id")
+	ErrUserAlreadyExists            = errors.New("user already exists")
+	ErrUserNotFound                 = errors.New("user not found")
+	ErrInvalidUserInput             = errors.New("invalid user input")
+	ErrSignatureDoesNotMatch        = errors.New("signature does not match")
+	ErrAuthorizationHeaderMalformed = errors.New("authorization header malformed")
+	ErrRequestTimeTooSkewed         = errors.New("request time too skewed")
+	ErrExpiredToken                 = errors.New("expired token")
+	ErrCredentialDisabled           = errors.New("credential disabled")
+	ErrAuthNotEnabled               = errors.New("authentication is not enabled")
+	ErrMasterKeyRequired            = errors.New("auth master key is required")
+	ErrInvalidMasterKey             = errors.New("invalid auth master key")
+	ErrNoAuthCredentials            = errors.New("no auth credentials found")
+	ErrUnsupportedAuthScheme        = errors.New("unsupported auth scheme")
+	ErrInvalidPresign               = errors.New("invalid presigned request")
+)

auth/middleware.go

@@ -0,0 +1,111 @@
+package auth
+
+import (
+	"errors"
+	"fs/metrics"
+	"log/slog"
+	"net"
+	"net/http"
+
+	"github.com/go-chi/chi/v5/middleware"
+)
+
+func Middleware(
+	svc *Service,
+	logger *slog.Logger,
+	auditEnabled bool,
+	onError func(http.ResponseWriter, *http.Request, error),
+) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			authCtx := RequestContext{Authenticated: false, AuthType: "none"}
+			if svc == nil || !svc.Config().Enabled {
+				metrics.Default.ObserveAuth("bypass", "disabled", "auth_disabled")
+				next.ServeHTTP(w, r.WithContext(WithRequestContext(r.Context(), authCtx)))
+				return
+			}
+
+			if r.URL.Path == "/healthz" {
+				metrics.Default.ObserveAuth("bypass", "none", "public_endpoint")
+				next.ServeHTTP(w, r.WithContext(WithRequestContext(r.Context(), authCtx)))
+				return
+			}
+
+			resolvedCtx, err := svc.AuthenticateRequest(r)
+			if err != nil {
+				metrics.Default.ObserveAuth("error", "sigv4", authErrorClass(err))
+				if auditEnabled && logger != nil {
+					requestID := middleware.GetReqID(r.Context())
+					attrs := []any{
+						"method", r.Method,
+						"path", r.URL.Path,
+						"remote_ip", clientIP(r.RemoteAddr),
+						"error", err.Error(),
+					}
+					if requestID != "" {
+						attrs = append(attrs, "request_id", requestID)
+					}
+					logger.Warn("auth_failed", attrs...)
+				}
+				if onError != nil {
+					onError(w, r, err)
+					return
+				}
+				http.Error(w, http.StatusText(http.StatusForbidden), http.StatusForbidden)
+				return
+			}
+
+			metrics.Default.ObserveAuth("ok", resolvedCtx.AuthType, "none")
+			if auditEnabled && logger != nil {
+				requestID := middleware.GetReqID(r.Context())
+				attrs := []any{
+					"method", r.Method,
+					"path", r.URL.Path,
+					"remote_ip", clientIP(r.RemoteAddr),
+					"access_key_id", resolvedCtx.AccessKeyID,
+					"auth_type", resolvedCtx.AuthType,
+				}
+				if requestID != "" {
+					attrs = append(attrs, "request_id", requestID)
+				}
+				logger.Info("auth_success", attrs...)
+			}
+			next.ServeHTTP(w, r.WithContext(WithRequestContext(r.Context(), resolvedCtx)))
+		})
+	}
+}
+
+func authErrorClass(err error) string {
+	switch {
+	case errors.Is(err, ErrInvalidAccessKeyID):
+		return "invalid_access_key"
+	case errors.Is(err, ErrSignatureDoesNotMatch):
+		return "signature_mismatch"
+	case errors.Is(err, ErrAuthorizationHeaderMalformed):
+		return "auth_header_malformed"
+	case errors.Is(err, ErrRequestTimeTooSkewed):
+		return "time_skew"
+	case errors.Is(err, ErrExpiredToken):
+		return "expired_token"
+	case errors.Is(err, ErrNoAuthCredentials):
+		return "missing_credentials"
+	case errors.Is(err, ErrUnsupportedAuthScheme):
+		return "unsupported_auth_scheme"
+	case errors.Is(err, ErrInvalidPresign):
+		return "invalid_presign"
+	case errors.Is(err, ErrCredentialDisabled):
+		return "credential_disabled"
+	case errors.Is(err, ErrAccessDenied):
+		return "access_denied"
+	default:
+		return "other"
+	}
+}
+
+func clientIP(remoteAddr string) string {
+	host, _, err := net.SplitHostPort(remoteAddr)
+	if err == nil && host != "" {
+		return host
+	}
+	return remoteAddr
+}

auth/policy.go

@@ -0,0 +1,66 @@
+package auth
+
+import (
+	"fs/models"
+	"strings"
+)
+
+func isAllowed(policy *models.AuthPolicy, target RequestTarget) bool {
+	if policy == nil {
+		return false
+	}
+
+	allowed := false
+	for _, stmt := range policy.Statements {
+		if !statementMatches(stmt, target) {
+			continue
+		}
+		effect := strings.ToLower(strings.TrimSpace(stmt.Effect))
+		if effect == "deny" {
+			return false
+		}
+		if effect == "allow" {
+			allowed = true
+		}
+	}
+	return allowed
+}
+
+func statementMatches(stmt models.AuthPolicyStatement, target RequestTarget) bool {
+	if !actionMatches(stmt.Actions, target.Action) {
+		return false
+	}
+	if !bucketMatches(stmt.Bucket, target.Bucket) {
+		return false
+	}
+	if target.Key == "" {
+		return true
+	}
+
+	prefix := strings.TrimSpace(stmt.Prefix)
+	if prefix == "" || prefix == "*" {
+		return true
+	}
+	return strings.HasPrefix(target.Key, prefix)
+}
+
+func actionMatches(actions []string, action Action) bool {
+	if len(actions) == 0 {
+		return false
+	}
+	for _, current := range actions {
+		normalized := strings.TrimSpace(current)
+		if normalized == "*" || normalized == "s3:*" || strings.EqualFold(normalized, string(action)) {
+			return true
+		}
+	}
+	return false
+}
+
+func bucketMatches(pattern, bucket string) bool {
+	pattern = strings.TrimSpace(pattern)
+	if pattern == "" || pattern == "*" {
+		return true
+	}
+	return pattern == bucket
+}

auth/service.go

@@ -0,0 +1,554 @@
+package auth
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"fs/metadata"
+	"fs/models"
+	"net/http"
+	"regexp"
+	"strings"
+	"time"
+)
+
+type Store interface {
+	GetAuthIdentity(accessKeyID string) (*models.AuthIdentity, error)
+	PutAuthIdentity(identity *models.AuthIdentity) error
+	DeleteAuthIdentity(accessKeyID string) error
+	ListAuthIdentities(limit int, after string) ([]models.AuthIdentity, string, error)
+	GetAuthPolicy(accessKeyID string) (*models.AuthPolicy, error)
+	PutAuthPolicy(policy *models.AuthPolicy) error
+	DeleteAuthPolicy(accessKeyID string) error
+}
+
+type CreateUserInput struct {
+	AccessKeyID string
+	SecretKey   string
+	Status      string
+	Policy      models.AuthPolicy
+}
+
+type UserSummary struct {
+	AccessKeyID string
+	Status      string
+	CreatedAt   int64
+	UpdatedAt   int64
+}
+
+type UserDetails struct {
+	AccessKeyID string
+	Status      string
+	CreatedAt   int64
+	UpdatedAt   int64
+	Policy      models.AuthPolicy
+}
+
+type CreateUserResult struct {
+	UserDetails
+	SecretKey string
+}
+
+var validAccessKeyID = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._-]{2,127}$`)
+
+type Service struct {
+	cfg       Config
+	store     Store
+	masterKey []byte
+	now       func() time.Time
+}
+
+func NewService(cfg Config, store Store) (*Service, error) {
+	if store == nil {
+		return nil, errors.New("auth store is required")
+	}
+
+	svc := &Service{
+		cfg:   cfg,
+		store: store,
+		now:   func() time.Time { return time.Now().UTC() },
+	}
+	if !cfg.Enabled {
+		return svc, nil
+	}
+
+	if strings.TrimSpace(cfg.MasterKey) == "" {
+		return nil, ErrMasterKeyRequired
+	}
+	masterKey, err := decodeMasterKey(cfg.MasterKey)
+	if err != nil {
+		return nil, err
+	}
+	svc.masterKey = masterKey
+	return svc, nil
+}
+
+func (s *Service) Config() Config {
+	return s.cfg
+}
+
+func (s *Service) EnsureBootstrap() error {
+	if !s.cfg.Enabled {
+		return nil
+	}
+	accessKey := strings.TrimSpace(s.cfg.BootstrapAccessKey)
+	secret := strings.TrimSpace(s.cfg.BootstrapSecretKey)
+	if accessKey == "" || secret == "" {
+		return nil
+	}
+
+	if len(accessKey) < 3 {
+		return errors.New("bootstrap access key must be at least 3 characters")
+	}
+	if len(secret) < 8 {
+		return errors.New("bootstrap secret key must be at least 8 characters")
+	}
+
+	now := s.now().Unix()
+	ciphertext, nonce, err := encryptSecret(s.masterKey, accessKey, secret)
+	if err != nil {
+		return err
+	}
+	identity := &models.AuthIdentity{
+		AccessKeyID: accessKey,
+		SecretEnc:   ciphertext,
+		SecretNonce: nonce,
+		EncAlg:      "AES-256-GCM",
+		KeyVersion:  "v1",
+		Status:      "active",
+		CreatedAt:   now,
+		UpdatedAt:   now,
+	}
+	if existing, err := s.store.GetAuthIdentity(accessKey); err == nil && existing != nil {
+		identity.CreatedAt = existing.CreatedAt
+	}
+	if err := s.store.PutAuthIdentity(identity); err != nil {
+		return err
+	}
+
+	policy := defaultBootstrapPolicy(accessKey)
+	if strings.TrimSpace(s.cfg.BootstrapPolicy) != "" {
+		parsed, err := parsePolicyJSON(s.cfg.BootstrapPolicy)
+		if err != nil {
+			return err
+		}
+		policy = parsed
+		policy.Principal = accessKey
+	}
+	return s.store.PutAuthPolicy(policy)
+}
+
+func (s *Service) AuthenticateRequest(r *http.Request) (RequestContext, error) {
+	if !s.cfg.Enabled {
+		return RequestContext{Authenticated: false, AuthType: "disabled"}, nil
+	}
+	input, err := parseSigV4(r)
+	if err != nil {
+		return RequestContext{}, err
+	}
+
+	if err := validateSigV4Input(s.now(), s.cfg, input); err != nil {
+		return RequestContext{}, err
+	}
+
+	identity, err := s.store.GetAuthIdentity(input.AccessKeyID)
+	if err != nil {
+		return RequestContext{}, ErrInvalidAccessKeyID
+	}
+	if !strings.EqualFold(identity.Status, "active") {
+		return RequestContext{}, ErrCredentialDisabled
+	}
+
+	secret, err := decryptSecret(s.masterKey, identity.AccessKeyID, identity.SecretEnc, identity.SecretNonce)
+	if err != nil {
+		return RequestContext{}, ErrSignatureDoesNotMatch
+	}
+	ok, err := signatureMatches(secret, r, input)
+	if err != nil {
+		return RequestContext{}, err
+	}
+	if !ok {
+		return RequestContext{}, ErrSignatureDoesNotMatch
+	}
+
+	authType := "sigv4-header"
+	if input.Presigned {
+		authType = "sigv4-presign"
+	}
+
+	if strings.HasPrefix(r.URL.Path, "/_admin/") {
+		return RequestContext{
+			Authenticated: true,
+			AccessKeyID:   identity.AccessKeyID,
+			AuthType:      authType,
+		}, nil
+	}
+
+	policy, err := s.store.GetAuthPolicy(identity.AccessKeyID)
+	if err != nil {
+		return RequestContext{}, ErrAccessDenied
+	}
+	target := resolveTarget(r)
+	if target.Action == "" {
+		return RequestContext{}, ErrAccessDenied
+	}
+	if !isAllowed(policy, target) {
+		return RequestContext{}, ErrAccessDenied
+	}
+
+	return RequestContext{
+		Authenticated: true,
+		AccessKeyID:   identity.AccessKeyID,
+		AuthType:      authType,
+	}, nil
+}
+
+func (s *Service) CreateUser(input CreateUserInput) (*CreateUserResult, error) {
+	if !s.cfg.Enabled {
+		return nil, ErrAuthNotEnabled
+	}
+
+	accessKeyID := strings.TrimSpace(input.AccessKeyID)
+	if !validAccessKeyID.MatchString(accessKeyID) {
+		return nil, fmt.Errorf("%w: invalid access key id", ErrInvalidUserInput)
+	}
+
+	secretKey := strings.TrimSpace(input.SecretKey)
+	if secretKey == "" {
+		generated, err := generateSecretKey(32)
+		if err != nil {
+			return nil, err
+		}
+		secretKey = generated
+	}
+	if len(secretKey) < 8 {
+		return nil, fmt.Errorf("%w: secret key must be at least 8 characters", ErrInvalidUserInput)
+	}
+
+	status := normalizeUserStatus(input.Status)
+	if status == "" {
+		return nil, fmt.Errorf("%w: status must be active or disabled", ErrInvalidUserInput)
+	}
+
+	policy, err := normalizePolicy(input.Policy, accessKeyID)
+	if err != nil {
+		return nil, err
+	}
+
+	existing, err := s.store.GetAuthIdentity(accessKeyID)
+	if err == nil && existing != nil {
+		return nil, ErrUserAlreadyExists
+	}
+	if err != nil && !errors.Is(err, metadata.ErrAuthIdentityNotFound) {
+		return nil, err
+	}
+
+	now := s.now().Unix()
+	ciphertext, nonce, err := encryptSecret(s.masterKey, accessKeyID, secretKey)
+	if err != nil {
+		return nil, err
+	}
+	identity := &models.AuthIdentity{
+		AccessKeyID: accessKeyID,
+		SecretEnc:   ciphertext,
+		SecretNonce: nonce,
+		EncAlg:      "AES-256-GCM",
+		KeyVersion:  "v1",
+		Status:      status,
+		CreatedAt:   now,
+		UpdatedAt:   now,
+	}
+	if err := s.store.PutAuthIdentity(identity); err != nil {
+		return nil, err
+	}
+	if err := s.store.PutAuthPolicy(&policy); err != nil {
+		return nil, err
+	}
+
+	return &CreateUserResult{
+		UserDetails: UserDetails{
+			AccessKeyID: accessKeyID,
+			Status:      status,
+			CreatedAt:   now,
+			UpdatedAt:   now,
+			Policy:      policy,
+		},
+		SecretKey: secretKey,
+	}, nil
+}
+
+func (s *Service) ListUsers(limit int, cursor string) ([]UserSummary, string, error) {
+	if !s.cfg.Enabled {
+		return nil, "", ErrAuthNotEnabled
+	}
+	if limit <= 0 {
+		limit = 100
+	}
+	if limit > 1000 {
+		limit = 1000
+	}
+
+	identities, nextCursor, err := s.store.ListAuthIdentities(limit, cursor)
+	if err != nil {
+		return nil, "", err
+	}
+	users := make([]UserSummary, 0, len(identities))
+	for _, identity := range identities {
+		users = append(users, UserSummary{
+			AccessKeyID: identity.AccessKeyID,
+			Status:      normalizeUserStatus(identity.Status),
+			CreatedAt:   identity.CreatedAt,
+			UpdatedAt:   identity.UpdatedAt,
+		})
+	}
+	return users, nextCursor, nil
+}
+
+func (s *Service) GetUser(accessKeyID string) (*UserDetails, error) {
+	if !s.cfg.Enabled {
+		return nil, ErrAuthNotEnabled
+	}
+	accessKeyID = strings.TrimSpace(accessKeyID)
+	if accessKeyID == "" {
+		return nil, fmt.Errorf("%w: access key id is required", ErrInvalidUserInput)
+	}
+
+	identity, err := s.store.GetAuthIdentity(accessKeyID)
+	if err != nil {
+		if errors.Is(err, metadata.ErrAuthIdentityNotFound) {
+			return nil, ErrUserNotFound
+		}
+		return nil, err
+	}
+	policy, err := s.store.GetAuthPolicy(accessKeyID)
+	if err != nil {
+		if errors.Is(err, metadata.ErrAuthPolicyNotFound) {
+			return nil, ErrUserNotFound
+		}
+		return nil, err
+	}
+
+	return &UserDetails{
+		AccessKeyID: identity.AccessKeyID,
+		Status:      normalizeUserStatus(identity.Status),
+		CreatedAt:   identity.CreatedAt,
+		UpdatedAt:   identity.UpdatedAt,
+		Policy:      *policy,
+	}, nil
+}
+
+func (s *Service) DeleteUser(accessKeyID string) error {
+	if !s.cfg.Enabled {
+		return ErrAuthNotEnabled
+	}
+	accessKeyID = strings.TrimSpace(accessKeyID)
+	if !validAccessKeyID.MatchString(accessKeyID) {
+		return fmt.Errorf("%w: invalid access key id", ErrInvalidUserInput)
+	}
+
+	bootstrap := strings.TrimSpace(s.cfg.BootstrapAccessKey)
+	if bootstrap != "" && accessKeyID == bootstrap {
+		return fmt.Errorf("%w: bootstrap user cannot be deleted", ErrInvalidUserInput)
+	}
+
+	if _, err := s.store.GetAuthIdentity(accessKeyID); err != nil {
+		if errors.Is(err, metadata.ErrAuthIdentityNotFound) {
+			return ErrUserNotFound
+		}
+		return err
+	}
+
+	if err := s.store.DeleteAuthIdentity(accessKeyID); err != nil {
+		if errors.Is(err, metadata.ErrAuthIdentityNotFound) {
+			return ErrUserNotFound
+		}
+		return err
+	}
+
+	if err := s.store.DeleteAuthPolicy(accessKeyID); err != nil && !errors.Is(err, metadata.ErrAuthPolicyNotFound) {
+		return err
+	}
+	return nil
+}
+
+func (s *Service) SetUserPolicy(accessKeyID string, policy models.AuthPolicy) (*UserDetails, error) {
+	if !s.cfg.Enabled {
+		return nil, ErrAuthNotEnabled
+	}
+	accessKeyID = strings.TrimSpace(accessKeyID)
+	if !validAccessKeyID.MatchString(accessKeyID) {
+		return nil, fmt.Errorf("%w: invalid access key id", ErrInvalidUserInput)
+	}
+
+	identity, err := s.store.GetAuthIdentity(accessKeyID)
+	if err != nil {
+		if errors.Is(err, metadata.ErrAuthIdentityNotFound) {
+			return nil, ErrUserNotFound
+		}
+		return nil, err
+	}
+
+	normalizedPolicy, err := normalizePolicy(policy, accessKeyID)
+	if err != nil {
+		return nil, err
+	}
+	if err := s.store.PutAuthPolicy(&normalizedPolicy); err != nil {
+		return nil, err
+	}
+
+	identity.UpdatedAt = s.now().Unix()
+	if err := s.store.PutAuthIdentity(identity); err != nil {
+		return nil, err
+	}
+
+	return &UserDetails{
+		AccessKeyID: identity.AccessKeyID,
+		Status:      normalizeUserStatus(identity.Status),
+		CreatedAt:   identity.CreatedAt,
+		UpdatedAt:   identity.UpdatedAt,
+		Policy:      normalizedPolicy,
+	}, nil
+}
+
+func (s *Service) SetUserStatus(accessKeyID, status string) (*UserDetails, error) {
+	if !s.cfg.Enabled {
+		return nil, ErrAuthNotEnabled
+	}
+	accessKeyID = strings.TrimSpace(accessKeyID)
+	if !validAccessKeyID.MatchString(accessKeyID) {
+		return nil, fmt.Errorf("%w: invalid access key id", ErrInvalidUserInput)
+	}
+
+	status = strings.TrimSpace(status)
+	if status == "" {
+		return nil, fmt.Errorf("%w: status is required", ErrInvalidUserInput)
+	}
+	normalizedStatus := normalizeUserStatus(status)
+	if normalizedStatus == "" {
+		return nil, fmt.Errorf("%w: status must be active or disabled", ErrInvalidUserInput)
+	}
+
+	identity, err := s.store.GetAuthIdentity(accessKeyID)
+	if err != nil {
+		if errors.Is(err, metadata.ErrAuthIdentityNotFound) {
+			return nil, ErrUserNotFound
+		}
+		return nil, err
+	}
+	identity.Status = normalizedStatus
+	identity.UpdatedAt = s.now().Unix()
+	if err := s.store.PutAuthIdentity(identity); err != nil {
+		return nil, err
+	}
+
+	policy, err := s.store.GetAuthPolicy(accessKeyID)
+	if err != nil {
+		if errors.Is(err, metadata.ErrAuthPolicyNotFound) {
+			return nil, ErrUserNotFound
+		}
+		return nil, err
+	}
+
+	return &UserDetails{
+		AccessKeyID: identity.AccessKeyID,
+		Status:      normalizeUserStatus(identity.Status),
+		CreatedAt:   identity.CreatedAt,
+		UpdatedAt:   identity.UpdatedAt,
+		Policy:      *policy,
+	}, nil
+}
+
+func parsePolicyJSON(raw string) (*models.AuthPolicy, error) {
+	policy := models.AuthPolicy{}
+	if err := json.Unmarshal([]byte(raw), &policy); err != nil {
+		return nil, fmt.Errorf("invalid bootstrap policy: %w", err)
+	}
+	if len(policy.Statements) == 0 {
+		return nil, errors.New("bootstrap policy must contain at least one statement")
+	}
+	return &policy, nil
+}
+
+func defaultBootstrapPolicy(principal string) *models.AuthPolicy {
+	return &models.AuthPolicy{
+		Principal: principal,
+		Statements: []models.AuthPolicyStatement{
+			{
+				Effect:  "allow",
+				Actions: []string{"s3:*"},
+				Bucket:  "*",
+				Prefix:  "*",
+			},
+		},
+	}
+}
+
+func generateSecretKey(length int) (string, error) {
+	if length <= 0 {
+		length = 32
+	}
+	buf := make([]byte, length)
+	if _, err := rand.Read(buf); err != nil {
+		return "", err
+	}
+	return base64.RawURLEncoding.EncodeToString(buf), nil
+}
+
+func normalizeUserStatus(raw string) string {
+	status := strings.ToLower(strings.TrimSpace(raw))
+	if status == "" {
+		return "active"
+	}
+	if status != "active" && status != "disabled" {
+		return ""
+	}
+	return status
+}
+
+func normalizePolicy(policy models.AuthPolicy, principal string) (models.AuthPolicy, error) {
+	if len(policy.Statements) == 0 {
+		return models.AuthPolicy{}, fmt.Errorf("%w: at least one policy statement is required", ErrInvalidUserInput)
+	}
+
+	out := models.AuthPolicy{
+		Principal:  principal,
+		Statements: make([]models.AuthPolicyStatement, 0, len(policy.Statements)),
+	}
+	for _, stmt := range policy.Statements {
+		effect := strings.ToLower(strings.TrimSpace(stmt.Effect))
+		if effect != "allow" && effect != "deny" {
+			return models.AuthPolicy{}, fmt.Errorf("%w: invalid policy effect %q", ErrInvalidUserInput, stmt.Effect)
+		}
+
+		actions := make([]string, 0, len(stmt.Actions))
+		for _, action := range stmt.Actions {
+			action = strings.TrimSpace(action)
+			if action == "" {
+				continue
+			}
+			actions = append(actions, action)
+		}
+		if len(actions) == 0 {
+			return models.AuthPolicy{}, fmt.Errorf("%w: policy statement must include at least one action", ErrInvalidUserInput)
+		}
+
+		bucket := strings.TrimSpace(stmt.Bucket)
+		if bucket == "" {
+			bucket = "*"
+		}
+		prefix := strings.TrimSpace(stmt.Prefix)
+		if prefix == "" {
+			prefix = "*"
+		}
+
+		out.Statements = append(out.Statements, models.AuthPolicyStatement{
+			Effect:  effect,
+			Actions: actions,
+			Bucket:  bucket,
+			Prefix:  prefix,
+		})
+	}
+	return out, nil
+}

auth/service_admin_test.go

@@ -0,0 +1,223 @@
+package auth
+
+import (
+	"encoding/base64"
+	"errors"
+	"fs/metadata"
+	"fs/models"
+	"path/filepath"
+	"testing"
+)
+
+func TestAdminCreateListGetUser(t *testing.T) {
+	meta, svc := newTestAuthService(t)
+
+	created, err := svc.CreateUser(CreateUserInput{
+		AccessKeyID: "backup-user",
+		Policy: models.AuthPolicy{
+			Statements: []models.AuthPolicyStatement{
+				{
+					Effect:  "allow",
+					Actions: []string{"s3:GetObject"},
+					Bucket:  "backup-bucket",
+					Prefix:  "restic/",
+				},
+			},
+		},
+	})
+	if err != nil {
+		t.Fatalf("CreateUser returned error: %v", err)
+	}
+	if created.SecretKey == "" {
+		t.Fatalf("CreateUser should return generated secret")
+	}
+	if created.AccessKeyID != "backup-user" {
+		t.Fatalf("CreateUser access key mismatch: got %q", created.AccessKeyID)
+	}
+	if created.Policy.Principal != "backup-user" {
+		t.Fatalf("policy principal mismatch: got %q", created.Policy.Principal)
+	}
+
+	users, nextCursor, err := svc.ListUsers(100, "")
+	if err != nil {
+		t.Fatalf("ListUsers returned error: %v", err)
+	}
+	if nextCursor != "" {
+		t.Fatalf("unexpected next cursor: %q", nextCursor)
+	}
+	if len(users) != 1 {
+		t.Fatalf("ListUsers returned %d users, want 1", len(users))
+	}
+	if users[0].AccessKeyID != "backup-user" {
+		t.Fatalf("ListUsers returned wrong user: %q", users[0].AccessKeyID)
+	}
+
+	got, err := svc.GetUser("backup-user")
+	if err != nil {
+		t.Fatalf("GetUser returned error: %v", err)
+	}
+	if got.AccessKeyID != "backup-user" {
+		t.Fatalf("GetUser access key mismatch: got %q", got.AccessKeyID)
+	}
+	if got.Policy.Principal != "backup-user" {
+		t.Fatalf("GetUser policy principal mismatch: got %q", got.Policy.Principal)
+	}
+	if len(got.Policy.Statements) != 1 {
+		t.Fatalf("GetUser policy statement count = %d, want 1", len(got.Policy.Statements))
+	}
+
+	_ = meta
+}
+
+func TestCreateUserDuplicateFails(t *testing.T) {
+	_, svc := newTestAuthService(t)
+
+	input := CreateUserInput{
+		AccessKeyID: "duplicate-user",
+		SecretKey:   "super-secret-1",
+		Policy: models.AuthPolicy{
+			Statements: []models.AuthPolicyStatement{
+				{Effect: "allow", Actions: []string{"s3:*"}, Bucket: "*", Prefix: "*"},
+			},
+		},
+	}
+	if _, err := svc.CreateUser(input); err != nil {
+		t.Fatalf("first CreateUser returned error: %v", err)
+	}
+	if _, err := svc.CreateUser(input); !errors.Is(err, ErrUserAlreadyExists) {
+		t.Fatalf("second CreateUser error = %v, want ErrUserAlreadyExists", err)
+	}
+}
+
+func TestCreateUserRejectsInvalidAccessKey(t *testing.T) {
+	_, svc := newTestAuthService(t)
+
+	_, err := svc.CreateUser(CreateUserInput{
+		AccessKeyID: "x",
+		SecretKey:   "super-secret-1",
+		Policy: models.AuthPolicy{
+			Statements: []models.AuthPolicyStatement{
+				{Effect: "allow", Actions: []string{"s3:*"}, Bucket: "*", Prefix: "*"},
+			},
+		},
+	})
+	if !errors.Is(err, ErrInvalidUserInput) {
+		t.Fatalf("CreateUser error = %v, want ErrInvalidUserInput", err)
+	}
+}
+
+func TestDeleteUser(t *testing.T) {
+	_, svc := newTestAuthService(t)
+
+	_, err := svc.CreateUser(CreateUserInput{
+		AccessKeyID: "delete-user",
+		SecretKey:   "super-secret-1",
+		Policy: models.AuthPolicy{
+			Statements: []models.AuthPolicyStatement{
+				{Effect: "allow", Actions: []string{"s3:*"}, Bucket: "*", Prefix: "*"},
+			},
+		},
+	})
+	if err != nil {
+		t.Fatalf("CreateUser returned error: %v", err)
+	}
+
+	if err := svc.DeleteUser("delete-user"); err != nil {
+		t.Fatalf("DeleteUser returned error: %v", err)
+	}
+	if _, err := svc.GetUser("delete-user"); !errors.Is(err, ErrUserNotFound) {
+		t.Fatalf("GetUser after delete error = %v, want ErrUserNotFound", err)
+	}
+}
+
+func TestDeleteBootstrapUserRejected(t *testing.T) {
+	_, svc := newTestAuthService(t)
+
+	if err := svc.DeleteUser("root-user"); !errors.Is(err, ErrInvalidUserInput) {
+		t.Fatalf("DeleteUser bootstrap error = %v, want ErrInvalidUserInput", err)
+	}
+}
+
+func TestSetUserPolicy(t *testing.T) {
+	_, svc := newTestAuthService(t)
+
+	_, err := svc.CreateUser(CreateUserInput{
+		AccessKeyID: "policy-user",
+		SecretKey:   "super-secret-1",
+		Policy: models.AuthPolicy{
+			Statements: []models.AuthPolicyStatement{
+				{Effect: "allow", Actions: []string{"s3:GetObject"}, Bucket: "b1", Prefix: "*"},
+			},
+		},
+	})
+	if err != nil {
+		t.Fatalf("CreateUser returned error: %v", err)
+	}
+
+	updated, err := svc.SetUserPolicy("policy-user", models.AuthPolicy{
+		Statements: []models.AuthPolicyStatement{
+			{Effect: "allow", Actions: []string{"s3:PutObject"}, Bucket: "b2", Prefix: "p/"},
+		},
+	})
+	if err != nil {
+		t.Fatalf("SetUserPolicy returned error: %v", err)
+	}
+	if len(updated.Policy.Statements) != 1 || updated.Policy.Statements[0].Actions[0] != "s3:PutObject" {
+		t.Fatalf("SetUserPolicy did not apply new policy: %+v", updated.Policy)
+	}
+}
+
+func TestSetUserStatus(t *testing.T) {
+	_, svc := newTestAuthService(t)
+
+	_, err := svc.CreateUser(CreateUserInput{
+		AccessKeyID: "status-user",
+		SecretKey:   "super-secret-1",
+		Policy: models.AuthPolicy{
+			Statements: []models.AuthPolicyStatement{
+				{Effect: "allow", Actions: []string{"s3:*"}, Bucket: "*", Prefix: "*"},
+			},
+		},
+	})
+	if err != nil {
+		t.Fatalf("CreateUser returned error: %v", err)
+	}
+
+	updated, err := svc.SetUserStatus("status-user", "disabled")
+	if err != nil {
+		t.Fatalf("SetUserStatus returned error: %v", err)
+	}
+	if updated.Status != "disabled" {
+		t.Fatalf("SetUserStatus status = %q, want disabled", updated.Status)
+	}
+}
+
+func newTestAuthService(t *testing.T) (*metadata.MetadataHandler, *Service) {
+	t.Helper()
+
+	dbPath := filepath.Join(t.TempDir(), "metadata.db")
+	meta, err := metadata.NewMetadataHandler(dbPath)
+	if err != nil {
+		t.Fatalf("NewMetadataHandler returned error: %v", err)
+	}
+	t.Cleanup(func() {
+		_ = meta.Close()
+	})
+
+	masterKey := base64.StdEncoding.EncodeToString(make([]byte, 32))
+	cfg := ConfigFromValues(
+		true,
+		"us-east-1",
+		0,
+		0,
+		masterKey,
+		"root-user",
+		"root-secret-123",
+		"",
+	)
+	svc, err := NewService(cfg, meta)
+	if err != nil {
+		t.Fatalf("NewService returned error: %v", err)
+	}
+	return meta, svc
+}

auth/sigv4.go

@@ -0,0 +1,372 @@
+package auth
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"net/http"
+	"net/url"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+)
+
+const (
+	sigV4Algorithm = "AWS4-HMAC-SHA256"
+)
+
+type sigV4Input struct {
+	AccessKeyID      string
+	Date             string
+	Region           string
+	Service          string
+	Scope            string
+	SignedHeaders    []string
+	SignedHeadersRaw string
+	SignatureHex     string
+	AmzDate          string
+	ExpiresSeconds   int
+	Presigned        bool
+}
+
+func parseSigV4(r *http.Request) (*sigV4Input, error) {
+	if r == nil {
+		return nil, fmt.Errorf("%w: nil request", ErrAuthorizationHeaderMalformed)
+	}
+	if strings.EqualFold(r.URL.Query().Get("X-Amz-Algorithm"), sigV4Algorithm) {
+		return parsePresignedSigV4(r)
+	}
+	return parseHeaderSigV4(r)
+}
+
+func parseHeaderSigV4(r *http.Request) (*sigV4Input, error) {
+	header := strings.TrimSpace(r.Header.Get("Authorization"))
+	if header == "" {
+		return nil, ErrNoAuthCredentials
+	}
+	if !strings.HasPrefix(header, sigV4Algorithm+" ") {
+		return nil, fmt.Errorf("%w: unsupported authorization algorithm", ErrUnsupportedAuthScheme)
+	}
+
+	params := parseAuthorizationParams(strings.TrimSpace(strings.TrimPrefix(header, sigV4Algorithm)))
+	credentialRaw := params["Credential"]
+	signedHeadersRaw := params["SignedHeaders"]
+	signatureHex := params["Signature"]
+	if credentialRaw == "" || signedHeadersRaw == "" || signatureHex == "" {
+		return nil, fmt.Errorf("%w: missing required authorization fields", ErrAuthorizationHeaderMalformed)
+	}
+
+	accessKeyID, date, region, service, scope, err := parseCredential(credentialRaw)
+	if err != nil {
+		return nil, err
+	}
+
+	amzDate := strings.TrimSpace(r.Header.Get("x-amz-date"))
+	if amzDate == "" {
+		return nil, fmt.Errorf("%w: x-amz-date is required", ErrAuthorizationHeaderMalformed)
+	}
+	signedHeaders := splitSignedHeaders(signedHeadersRaw)
+	if len(signedHeaders) == 0 {
+		return nil, fmt.Errorf("%w: signed headers are required", ErrAuthorizationHeaderMalformed)
+	}
+
+	return &sigV4Input{
+		AccessKeyID:      accessKeyID,
+		Date:             date,
+		Region:           region,
+		Service:          service,
+		Scope:            scope,
+		SignedHeaders:    signedHeaders,
+		SignedHeadersRaw: strings.ToLower(strings.TrimSpace(signedHeadersRaw)),
+		SignatureHex:     strings.ToLower(strings.TrimSpace(signatureHex)),
+		AmzDate:          amzDate,
+		Presigned:        false,
+	}, nil
+}
+
+func parsePresignedSigV4(r *http.Request) (*sigV4Input, error) {
+	query := r.URL.Query()
+	if !strings.EqualFold(query.Get("X-Amz-Algorithm"), sigV4Algorithm) {
+		return nil, fmt.Errorf("%w: invalid X-Amz-Algorithm", ErrInvalidPresign)
+	}
+
+	credentialRaw := strings.TrimSpace(query.Get("X-Amz-Credential"))
+	signedHeadersRaw := strings.TrimSpace(query.Get("X-Amz-SignedHeaders"))
+	signatureHex := strings.TrimSpace(query.Get("X-Amz-Signature"))
+	amzDate := strings.TrimSpace(query.Get("X-Amz-Date"))
+	expiresRaw := strings.TrimSpace(query.Get("X-Amz-Expires"))
+	if credentialRaw == "" || signedHeadersRaw == "" || signatureHex == "" || amzDate == "" || expiresRaw == "" {
+		return nil, fmt.Errorf("%w: missing presigned query fields", ErrInvalidPresign)
+	}
+	expires, err := strconv.Atoi(expiresRaw)
+	if err != nil || expires < 0 {
+		return nil, fmt.Errorf("%w: invalid X-Amz-Expires", ErrInvalidPresign)
+	}
+
+	accessKeyID, date, region, service, scope, err := parseCredential(credentialRaw)
+	if err != nil {
+		return nil, err
+	}
+	signedHeaders := splitSignedHeaders(signedHeadersRaw)
+	if len(signedHeaders) == 0 {
+		return nil, fmt.Errorf("%w: signed headers are required", ErrInvalidPresign)
+	}
+
+	return &sigV4Input{
+		AccessKeyID:      accessKeyID,
+		Date:             date,
+		Region:           region,
+		Service:          service,
+		Scope:            scope,
+		SignedHeaders:    signedHeaders,
+		SignedHeadersRaw: strings.ToLower(strings.TrimSpace(signedHeadersRaw)),
+		SignatureHex:     strings.ToLower(signatureHex),
+		AmzDate:          amzDate,
+		ExpiresSeconds:   expires,
+		Presigned:        true,
+	}, nil
+}
+
+func parseCredential(raw string) (accessKeyID string, date string, region string, service string, scope string, err error) {
+	parts := strings.Split(strings.TrimSpace(raw), "/")
+	if len(parts) != 5 {
+		return "", "", "", "", "", fmt.Errorf("%w: invalid credential scope", ErrAuthorizationHeaderMalformed)
+	}
+	accessKeyID = strings.TrimSpace(parts[0])
+	date = strings.TrimSpace(parts[1])
+	region = strings.TrimSpace(parts[2])
+	service = strings.TrimSpace(parts[3])
+	terminal := strings.TrimSpace(parts[4])
+	if accessKeyID == "" || date == "" || region == "" || service == "" || terminal != "aws4_request" {
+		return "", "", "", "", "", fmt.Errorf("%w: invalid credential scope", ErrAuthorizationHeaderMalformed)
+	}
+	scope = strings.Join(parts[1:], "/")
+	return accessKeyID, date, region, service, scope, nil
+}
+
+func splitSignedHeaders(raw string) []string {
+	raw = strings.ToLower(strings.TrimSpace(raw))
+	if raw == "" {
+		return nil
+	}
+	parts := strings.Split(raw, ";")
+	headers := make([]string, 0, len(parts))
+	for _, current := range parts {
+		current = strings.TrimSpace(current)
+		if current == "" {
+			continue
+		}
+		headers = append(headers, current)
+	}
+	return headers
+}
+
+func parseAuthorizationParams(raw string) map[string]string {
+	params := make(map[string]string)
+	raw = strings.TrimSpace(raw)
+	raw = strings.TrimPrefix(raw, " ")
+	for _, token := range strings.Split(raw, ",") {
+		token = strings.TrimSpace(token)
+		key, value, found := strings.Cut(token, "=")
+		if !found {
+			continue
+		}
+		params[strings.TrimSpace(key)] = strings.TrimSpace(value)
+	}
+	return params
+}
+
+func validateSigV4Input(now time.Time, cfg Config, input *sigV4Input) error {
+	if input == nil {
+		return fmt.Errorf("%w: empty signature input", ErrAuthorizationHeaderMalformed)
+	}
+	if !strings.EqualFold(input.Service, "s3") {
+		return fmt.Errorf("%w: unsupported service", ErrAuthorizationHeaderMalformed)
+	}
+	if !strings.EqualFold(input.Region, cfg.Region) {
+		return fmt.Errorf("%w: region mismatch", ErrAuthorizationHeaderMalformed)
+	}
+
+	requestTime, err := time.Parse("20060102T150405Z", input.AmzDate)
+	if err != nil {
+		return fmt.Errorf("%w: invalid x-amz-date", ErrAuthorizationHeaderMalformed)
+	}
+	delta := now.Sub(requestTime)
+	if delta > cfg.ClockSkew || delta < -cfg.ClockSkew {
+		return ErrRequestTimeTooSkewed
+	}
+
+	if input.Presigned {
+		if input.ExpiresSeconds > int(cfg.MaxPresignDuration.Seconds()) {
+			return fmt.Errorf("%w: presign expires too large", ErrInvalidPresign)
+		}
+		expiresAt := requestTime.Add(time.Duration(input.ExpiresSeconds) * time.Second)
+		if now.After(expiresAt) {
+			return ErrExpiredToken
+		}
+	}
+	return nil
+}
+
+func signatureMatches(secret string, r *http.Request, input *sigV4Input) (bool, error) {
+	payloadHash := resolvePayloadHash(r, input.Presigned)
+	canonicalRequest, err := buildCanonicalRequest(r, input.SignedHeaders, payloadHash, input.Presigned)
+	if err != nil {
+		return false, err
+	}
+	stringToSign := buildStringToSign(input.AmzDate, input.Scope, canonicalRequest)
+	signingKey := deriveSigningKey(secret, input.Date, input.Region, input.Service)
+	expectedSig := hex.EncodeToString(hmacSHA256(signingKey, stringToSign))
+	return hmac.Equal([]byte(expectedSig), []byte(input.SignatureHex)), nil
+}
+
+func resolvePayloadHash(r *http.Request, presigned bool) string {
+	if presigned {
+		return "UNSIGNED-PAYLOAD"
+	}
+	hash := strings.TrimSpace(r.Header.Get("x-amz-content-sha256"))
+	if hash == "" {
+		return "UNSIGNED-PAYLOAD"
+	}
+	return hash
+}
+
+func buildCanonicalRequest(r *http.Request, signedHeaders []string, payloadHash string, presigned bool) (string, error) {
+	canonicalURI := canonicalPath(r.URL)
+	canonicalQuery := canonicalQueryString(r.URL.RawQuery, presigned)
+	canonicalHeaders, signedHeadersRaw, err := canonicalHeadersForRequest(r, signedHeaders)
+	if err != nil {
+		return "", err
+	}
+
+	return strings.Join([]string{
+		r.Method,
+		canonicalURI,
+		canonicalQuery,
+		canonicalHeaders,
+		signedHeadersRaw,
+		payloadHash,
+	}, "\n"), nil
+}
+
+func canonicalPath(u *url.URL) string {
+	if u == nil {
+		return "/"
+	}
+	path := u.EscapedPath()
+	if path == "" {
+		return "/"
+	}
+	return path
+}
+
+type queryPair struct {
+	Key   string
+	Value string
+}
+
+func canonicalQueryString(rawQuery string, presigned bool) string {
+	if rawQuery == "" {
+		return ""
+	}
+	values, _ := url.ParseQuery(rawQuery)
+	pairs := make([]queryPair, 0)
+	for key, valueList := range values {
+		if presigned && strings.EqualFold(key, "X-Amz-Signature") {
+			continue
+		}
+		if len(valueList) == 0 {
+			pairs = append(pairs, queryPair{Key: key, Value: ""})
+			continue
+		}
+		for _, value := range valueList {
+			pairs = append(pairs, queryPair{Key: key, Value: value})
+		}
+	}
+	sort.Slice(pairs, func(i, j int) bool {
+		if pairs[i].Key == pairs[j].Key {
+			return pairs[i].Value < pairs[j].Value
+		}
+		return pairs[i].Key < pairs[j].Key
+	})
+
+	encoded := make([]string, 0, len(pairs))
+	for _, pair := range pairs {
+		encoded = append(encoded, awsEncodeQuery(pair.Key)+"="+awsEncodeQuery(pair.Value))
+	}
+	return strings.Join(encoded, "&")
+}
+
+func awsEncodeQuery(value string) string {
+	encoded := url.QueryEscape(value)
+	encoded = strings.ReplaceAll(encoded, "+", "%20")
+	encoded = strings.ReplaceAll(encoded, "*", "%2A")
+	encoded = strings.ReplaceAll(encoded, "%7E", "~")
+	return encoded
+}
+
+func canonicalHeadersForRequest(r *http.Request, signedHeaders []string) (canonical string, signedRaw string, err error) {
+	if len(signedHeaders) == 0 {
+		return "", "", fmt.Errorf("%w: empty signed headers", ErrAuthorizationHeaderMalformed)
+	}
+
+	normalized := make([]string, 0, len(signedHeaders))
+	lines := make([]string, 0, len(signedHeaders))
+	for _, headerName := range signedHeaders {
+		headerName = strings.ToLower(strings.TrimSpace(headerName))
+		if headerName == "" {
+			continue
+		}
+		var value string
+		if headerName == "host" {
+			value = r.Host
+		} else {
+			values, ok := r.Header[http.CanonicalHeaderKey(headerName)]
+			if !ok || len(values) == 0 {
+				return "", "", fmt.Errorf("%w: missing signed header %q", ErrAuthorizationHeaderMalformed, headerName)
+			}
+			value = strings.Join(values, ",")
+		}
+		value = normalizeHeaderValue(value)
+		normalized = append(normalized, headerName)
+		lines = append(lines, headerName+":"+value)
+	}
+
+	if len(lines) == 0 {
+		return "", "", fmt.Errorf("%w: no valid signed headers", ErrAuthorizationHeaderMalformed)
+	}
+	signedRaw = strings.Join(normalized, ";")
+	canonical = strings.Join(lines, "\n") + "\n"
+	return canonical, signedRaw, nil
+}
+
+func normalizeHeaderValue(value string) string {
+	value = strings.TrimSpace(value)
+	parts := strings.Fields(value)
+	return strings.Join(parts, " ")
+}
+
+func buildStringToSign(amzDate string, scope string, canonicalRequest string) string {
+	canonicalHash := sha256.Sum256([]byte(canonicalRequest))
+	return strings.Join([]string{
+		sigV4Algorithm,
+		amzDate,
+		scope,
+		hex.EncodeToString(canonicalHash[:]),
+	}, "\n")
+}
+
+func deriveSigningKey(secret, date, region, service string) []byte {
+	kDate := hmacSHA256([]byte("AWS4"+secret), date)
+	kRegion := hmacSHA256(kDate, region)
+	kService := hmacSHA256(kRegion, service)
+	return hmacSHA256(kService, "aws4_request")
+}
+
+func hmacSHA256(key []byte, value string) []byte {
+	mac := hmac.New(sha256.New, key)
+	_, _ = mac.Write([]byte(value))
+	return mac.Sum(nil)
+}

docs/admin-api-openapi.yaml

@@ -0,0 +1,336 @@
+openapi: 3.1.0
+info:
+  title: fs Admin API
+  version: 1.0.0
+  description: |
+    JSON admin API for managing local users and policies.
+
+    Notes:
+    - Base path is `/_admin/v1`.
+    - Requests must be AWS SigV4 signed.
+    - Only the bootstrap access key is authorized for admin endpoints.
+servers:
+  - url: http://localhost:2600
+    description: Local development
+security:
+  - AwsSigV4: []
+paths:
+  /_admin/v1/users:
+    post:
+      summary: Create user
+      operationId: createUser
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/CreateUserRequest'
+      responses:
+        '201':
+          description: User created
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/UserResponse'
+        '400':
+          $ref: '#/components/responses/InvalidRequest'
+        '403':
+          $ref: '#/components/responses/Forbidden'
+        '409':
+          $ref: '#/components/responses/UserAlreadyExists'
+        '503':
+          $ref: '#/components/responses/AuthDisabled'
+        '500':
+          $ref: '#/components/responses/InternalError'
+    get:
+      summary: List users
+      operationId: listUsers
+      parameters:
+        - name: limit
+          in: query
+          required: false
+          schema:
+            type: integer
+            minimum: 1
+            maximum: 1000
+            default: 100
+        - name: cursor
+          in: query
+          required: false
+          schema:
+            type: string
+      responses:
+        '200':
+          description: User summaries
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/UserListResponse'
+        '400':
+          $ref: '#/components/responses/InvalidRequest'
+        '403':
+          $ref: '#/components/responses/Forbidden'
+        '503':
+          $ref: '#/components/responses/AuthDisabled'
+        '500':
+          $ref: '#/components/responses/InternalError'
+
+  /_admin/v1/users/{accessKeyId}:
+    get:
+      summary: Get user with policy
+      operationId: getUser
+      parameters:
+        - $ref: '#/components/parameters/AccessKeyId'
+      responses:
+        '200':
+          description: User details
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/UserResponse'
+        '403':
+          $ref: '#/components/responses/Forbidden'
+        '404':
+          $ref: '#/components/responses/UserNotFound'
+        '503':
+          $ref: '#/components/responses/AuthDisabled'
+        '500':
+          $ref: '#/components/responses/InternalError'
+    delete:
+      summary: Delete user
+      operationId: deleteUser
+      parameters:
+        - $ref: '#/components/parameters/AccessKeyId'
+      responses:
+        '204':
+          description: User deleted
+        '400':
+          $ref: '#/components/responses/InvalidRequest'
+        '403':
+          $ref: '#/components/responses/Forbidden'
+        '404':
+          $ref: '#/components/responses/UserNotFound'
+        '503':
+          $ref: '#/components/responses/AuthDisabled'
+        '500':
+          $ref: '#/components/responses/InternalError'
+
+  /_admin/v1/users/{accessKeyId}/policy:
+    put:
+      summary: Replace user policy
+      operationId: setUserPolicy
+      parameters:
+        - $ref: '#/components/parameters/AccessKeyId'
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/SetPolicyRequest'
+      responses:
+        '200':
+          description: User details with updated policy
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/UserResponse'
+        '400':
+          $ref: '#/components/responses/InvalidRequest'
+        '403':
+          $ref: '#/components/responses/Forbidden'
+        '404':
+          $ref: '#/components/responses/UserNotFound'
+        '503':
+          $ref: '#/components/responses/AuthDisabled'
+        '500':
+          $ref: '#/components/responses/InternalError'
+
+  /_admin/v1/users/{accessKeyId}/status:
+    put:
+      summary: Set user status
+      operationId: setUserStatus
+      parameters:
+        - $ref: '#/components/parameters/AccessKeyId'
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/SetStatusRequest'
+      responses:
+        '200':
+          description: User details with updated status
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/UserResponse'
+        '400':
+          $ref: '#/components/responses/InvalidRequest'
+        '403':
+          $ref: '#/components/responses/Forbidden'
+        '404':
+          $ref: '#/components/responses/UserNotFound'
+        '503':
+          $ref: '#/components/responses/AuthDisabled'
+        '500':
+          $ref: '#/components/responses/InternalError'
+
+components:
+  securitySchemes:
+    AwsSigV4:
+      type: apiKey
+      in: header
+      name: Authorization
+      description: |
+        AWS Signature Version 4 headers are required (`Authorization`, `x-amz-date`,
+        and for payload-signed requests `x-amz-content-sha256`).
+        Only bootstrap credential is authorized for admin endpoints.
+  parameters:
+    AccessKeyId:
+      name: accessKeyId
+      in: path
+      required: true
+      schema:
+        type: string
+      description: User access key ID
+  responses:
+    InvalidRequest:
+      description: Invalid request input
+      content:
+        application/json:
+          schema:
+            $ref: '#/components/schemas/AdminError'
+    Forbidden:
+      description: Authenticated but not allowed
+      content:
+        application/json:
+          schema:
+            $ref: '#/components/schemas/AdminError'
+    UserAlreadyExists:
+      description: User already exists
+      content:
+        application/json:
+          schema:
+            $ref: '#/components/schemas/AdminError'
+    UserNotFound:
+      description: User not found
+      content:
+        application/json:
+          schema:
+            $ref: '#/components/schemas/AdminError'
+    AuthDisabled:
+      description: Authentication subsystem disabled
+      content:
+        application/json:
+          schema:
+            $ref: '#/components/schemas/AdminError'
+    InternalError:
+      description: Internal server error
+      content:
+        application/json:
+          schema:
+            $ref: '#/components/schemas/AdminError'
+  schemas:
+    AdminError:
+      type: object
+      properties:
+        code:
+          type: string
+        message:
+          type: string
+        requestId:
+          type: string
+      required: [code, message]
+    PolicyStatement:
+      type: object
+      properties:
+        effect:
+          type: string
+          enum: [allow, deny]
+        actions:
+          type: array
+          items:
+            type: string
+          minItems: 1
+        bucket:
+          type: string
+          default: "*"
+        prefix:
+          type: string
+          default: "*"
+      required: [effect, actions]
+    Policy:
+      type: object
+      properties:
+        principal:
+          type: string
+          description: Server-managed; overwritten with target access key ID.
+        statements:
+          type: array
+          items:
+            $ref: '#/components/schemas/PolicyStatement'
+          minItems: 1
+      required: [statements]
+    CreateUserRequest:
+      type: object
+      properties:
+        accessKeyId:
+          type: string
+        secretKey:
+          type: string
+          description: If omitted, server generates one.
+        status:
+          type: string
+          enum: [active, disabled]
+          default: active
+        policy:
+          $ref: '#/components/schemas/Policy'
+      required: [accessKeyId, policy]
+    SetPolicyRequest:
+      type: object
+      properties:
+        policy:
+          $ref: '#/components/schemas/Policy'
+      required: [policy]
+    SetStatusRequest:
+      type: object
+      properties:
+        status:
+          type: string
+          enum: [active, disabled]
+      required: [status]
+    UserListItem:
+      type: object
+      properties:
+        accessKeyId:
+          type: string
+        status:
+          type: string
+          enum: [active, disabled]
+        createdAt:
+          type: integer
+          format: int64
+        updatedAt:
+          type: integer
+          format: int64
+      required: [accessKeyId, status, createdAt, updatedAt]
+    UserListResponse:
+      type: object
+      properties:
+        items:
+          type: array
+          items:
+            $ref: '#/components/schemas/UserListItem'
+        nextCursor:
+          type: string
+      required: [items]
+    UserResponse:
+      allOf:
+        - $ref: '#/components/schemas/UserListItem'
+        - type: object
+          properties:
+            policy:
+              $ref: '#/components/schemas/Policy'
+            secretKey:
+              type: string
+              description: Returned only on create.

docs/s3-compatibility.md

@@ -0,0 +1,53 @@
+# S3 Compatibility Matrix
+
+This project is S3-compatible for a focused subset of operations.
+
+## Implemented
+
+### Service and account
+- `GET /` list buckets
+
+### Bucket
+- `PUT /{bucket}` create bucket
+- `HEAD /{bucket}` head bucket
+- `DELETE /{bucket}` delete bucket (must be empty)
+- `GET /{bucket}?list-type=2...` list objects v2
+- `GET /{bucket}?location` get bucket location
+- `POST /{bucket}?delete` delete multiple objects
+
+### Object
+- `PUT /{bucket}/{key}` put object
+- `GET /{bucket}/{key}` get object
+- `HEAD /{bucket}/{key}` head object
+- `DELETE /{bucket}/{key}` delete object
+- `GET /{bucket}/{key}` supports single-range requests
+
+### Multipart upload
+- `POST /{bucket}/{key}?uploads` initiate
+- `PUT /{bucket}/{key}?uploadId=...&partNumber=N` upload part
+- `GET /{bucket}/{key}?uploadId=...` list parts
+- `POST /{bucket}/{key}?uploadId=...` complete
+- `DELETE /{bucket}/{key}?uploadId=...` abort
+
+### Authentication
+- AWS SigV4 header auth
+- AWS SigV4 presigned query auth
+- `aws-chunked` payload decode for streaming uploads
+
+## Partially Implemented / Differences
+- Exact parity with AWS S3 error codes/headers is still evolving.
+- Some S3 edge-case behaviors may differ (especially uncommon query/header combinations).
+- Admin API is custom JSON (`/_admin/v1/*`).
+
+## Not Implemented (Current)
+- Bucket versioning
+- Lifecycle rules
+- Replication
+- Object lock / legal hold / retention
+- SSE-S3 / SSE-KMS / SSE-C
+- ACL APIs and IAM-compatible policy APIs
+- STS / temporary credentials
+- Event notifications
+- Tagging APIs
+- CORS APIs
+- Website hosting APIs

logging/logging.go

@@ -1,6 +1,7 @@
 package logging
 
 import (
+	"fs/metrics"
 	"log/slog"
 	"net/http"
 	"os"
@@ -9,6 +10,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/go-chi/chi/v5"
 	"github.com/go-chi/chi/v5/middleware"
 )
 
@@ -86,6 +88,11 @@ func HTTPMiddleware(logger *slog.Logger, cfg Config) func(http.Handler) http.Han
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			start := time.Now()
 			ww := middleware.NewWrapResponseWriter(w, r.ProtoMajor)
+			op := metricOperationLabel(r)
+			metrics.Default.IncHTTPInFlightOp(op)
+			defer func() {
+				metrics.Default.DecHTTPInFlightOp(op)
+			}()
 			requestID := middleware.GetReqID(r.Context())
 			if requestID != "" {
 				ww.Header().Set("x-amz-request-id", requestID)
@@ -93,15 +100,18 @@ func HTTPMiddleware(logger *slog.Logger, cfg Config) func(http.Handler) http.Han
 
 			next.ServeHTTP(ww, r)
 
-			if !cfg.Audit && !cfg.DebugMode {
-				return
-			}
-
 			elapsed := time.Since(start)
 			status := ww.Status()
 			if status == 0 {
 				status = http.StatusOK
 			}
+			route := metricRouteLabel(r)
+			metrics.Default.ObserveHTTPRequestDetailed(r.Method, route, op, status, elapsed, ww.BytesWritten())
+
+			if !cfg.Audit && !cfg.DebugMode {
+				return
+			}
+
 			attrs := []any{
 				"method", r.Method,
 				"path", r.URL.Path,
@@ -131,6 +141,46 @@ func HTTPMiddleware(logger *slog.Logger, cfg Config) func(http.Handler) http.Han
 	}
 }
 
+func metricRouteLabel(r *http.Request) string {
+	if r == nil || r.URL == nil {
+		return "/unknown"
+	}
+
+	if routeCtx := chi.RouteContext(r.Context()); routeCtx != nil {
+		if pattern := strings.TrimSpace(routeCtx.RoutePattern()); pattern != "" {
+			return pattern
+		}
+	}
+
+	path := strings.TrimSpace(r.URL.Path)
+	if path == "" || path == "/" {
+		return "/"
+	}
+	if path == "/healthz" || path == "/metrics" {
+		return path
+	}
+
+	trimmed := strings.Trim(path, "/")
+	if trimmed == "" {
+		return "/"
+	}
+	if !strings.Contains(trimmed, "/") {
+		return "/{bucket}"
+	}
+	return "/{bucket}/*"
+}
+
+func metricOperationLabel(r *http.Request) string {
+	if r == nil {
+		return "other"
+	}
+	isDeletePost := false
+	if r.Method == http.MethodPost && r.URL != nil {
+		_, isDeletePost = r.URL.Query()["delete"]
+	}
+	return metrics.NormalizeHTTPOperation(r.Method, isDeletePost)
+}
+
 func envBool(key string, defaultValue bool) bool {
 	raw := os.Getenv(key)
 	if raw == "" {

logging/logging_metrics_test.go

@@ -0,0 +1,30 @@
+package logging
+
+import (
+	"net/http/httptest"
+	"testing"
+)
+
+func TestMetricRouteLabelFallbacks(t *testing.T) {
+	testCases := []struct {
+		name string
+		path string
+		want string
+	}{
+		{name: "root", path: "/", want: "/"},
+		{name: "health", path: "/healthz", want: "/healthz"},
+		{name: "metrics", path: "/metrics", want: "/metrics"},
+		{name: "bucket", path: "/some-bucket", want: "/{bucket}"},
+		{name: "object", path: "/some-bucket/private/path/file.jpg", want: "/{bucket}/*"},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			req := httptest.NewRequest("GET", tc.path, nil)
+			got := metricRouteLabel(req)
+			if got != tc.want {
+				t.Fatalf("metricRouteLabel(%q) = %q, want %q", tc.path, got, tc.want)
+			}
+		})
+	}
+}

main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"fs/api"
+	"fs/auth"
 	"fs/logging"
 	"fs/metadata"
 	"fs/service"
@@ -19,6 +20,16 @@ import (
 func main() {
 	config := utils.NewConfig()
 	logConfig := logging.ConfigFromValues(config.LogLevel, config.LogFormat, config.AuditLog)
+	authConfig := auth.ConfigFromValues(
+		config.AuthEnabled,
+		config.AuthRegion,
+		config.AuthSkew,
+		config.AuthMaxPresign,
+		config.AuthMasterKey,
+		config.AuthBootstrapAccessKey,
+		config.AuthBootstrapSecretKey,
+		config.AuthBootstrapPolicy,
+	)
 	logger := logging.NewLogger(logConfig)
 	logger.Info("boot",
 		"log_level", logConfig.LevelName,
@@ -26,6 +37,9 @@ func main() {
 		"audit_log", logConfig.Audit,
 		"data_path", config.DataPath,
 		"multipart_retention_hours", int(config.MultipartCleanupRetention/time.Hour),
+		"auth_enabled", authConfig.Enabled,
+		"auth_region", authConfig.Region,
+		"admin_api_enabled", config.AdminAPIEnabled,
 	)
 
 	if err := os.MkdirAll(config.DataPath, 0o755); err != nil {
@@ -47,7 +61,19 @@ func main() {
 	}
 
 	objectService := service.NewObjectService(metadataHandler, blobHandler, config.MultipartCleanupRetention)
-	handler := api.NewHandler(objectService, logger, logConfig)
+	authService, err := auth.NewService(authConfig, metadataHandler)
+	if err != nil {
+		_ = metadataHandler.Close()
+		logger.Error("failed_to_initialize_auth_service", "error", err)
+		return
+	}
+	if err := authService.EnsureBootstrap(); err != nil {
+		_ = metadataHandler.Close()
+		logger.Error("failed_to_ensure_bootstrap_auth_identity", "error", err)
+		return
+	}
+
+	handler := api.NewHandler(objectService, logger, logConfig, authService, config.AdminAPIEnabled)
 	addr := config.Address + ":" + strconv.Itoa(config.Port)
 
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)

metadata/metadata.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"fs/metrics"
 	"fs/models"
 	"net"
 	"regexp"
@@ -23,17 +24,21 @@ type MetadataHandler struct {
 var systemIndex = []byte("__SYSTEM_BUCKETS__")
 var multipartUploadIndex = []byte("__MULTIPART_UPLOADS__")
 var multipartUploadPartsIndex = []byte("__MULTIPART_UPLOAD_PARTS__")
+var authIdentitiesIndex = []byte("__AUTH_IDENTITIES__")
+var authPoliciesIndex = []byte("__AUTH_POLICIES__")
 
 var validBucketName = regexp.MustCompile(`^[a-z0-9.-]+$`)
 
 var (
-	ErrInvalidBucketName   = errors.New("invalid bucket name")
-	ErrBucketAlreadyExists = errors.New("bucket already exists")
-	ErrBucketNotFound      = errors.New("bucket not found")
-	ErrBucketNotEmpty      = errors.New("bucket not empty")
-	ErrObjectNotFound      = errors.New("object not found")
-	ErrMultipartNotFound   = errors.New("multipart upload not found")
-	ErrMultipartNotPending = errors.New("multipart upload is not pending")
+	ErrInvalidBucketName    = errors.New("invalid bucket name")
+	ErrBucketAlreadyExists  = errors.New("bucket already exists")
+	ErrBucketNotFound       = errors.New("bucket not found")
+	ErrBucketNotEmpty       = errors.New("bucket not empty")
+	ErrObjectNotFound       = errors.New("object not found")
+	ErrMultipartNotFound    = errors.New("multipart upload not found")
+	ErrMultipartNotPending  = errors.New("multipart upload is not pending")
+	ErrAuthIdentityNotFound = errors.New("auth identity not found")
+	ErrAuthPolicyNotFound   = errors.New("auth policy not found")
 )
 
 func NewMetadataHandler(dbPath string) (*MetadataHandler, error) {
@@ -43,7 +48,7 @@ func NewMetadataHandler(dbPath string) (*MetadataHandler, error) {
 	}
 	h := &MetadataHandler{db: db}
 
-	err = h.db.Update(func(tx *bbolt.Tx) error {
+	err = h.update(func(tx *bbolt.Tx) error {
 		_, err := tx.CreateBucketIfNotExists(systemIndex)
 		return err
 	})
@@ -51,7 +56,7 @@ func NewMetadataHandler(dbPath string) (*MetadataHandler, error) {
 		_ = db.Close()
 		return nil, err
 	}
-	err = h.db.Update(func(tx *bbolt.Tx) error {
+	err = h.update(func(tx *bbolt.Tx) error {
 		_, err := tx.CreateBucketIfNotExists(multipartUploadIndex)
 		return err
 	})
@@ -59,7 +64,7 @@ func NewMetadataHandler(dbPath string) (*MetadataHandler, error) {
 		_ = db.Close()
 		return nil, err
 	}
-	err = h.db.Update(func(tx *bbolt.Tx) error {
+	err = h.update(func(tx *bbolt.Tx) error {
 		_, err := tx.CreateBucketIfNotExists(multipartUploadPartsIndex)
 		return err
 	})
@@ -67,6 +72,22 @@ func NewMetadataHandler(dbPath string) (*MetadataHandler, error) {
 		_ = db.Close()
 		return nil, err
 	}
+	err = h.update(func(tx *bbolt.Tx) error {
+		_, err := tx.CreateBucketIfNotExists(authIdentitiesIndex)
+		return err
+	})
+	if err != nil {
+		_ = db.Close()
+		return nil, err
+	}
+	err = h.update(func(tx *bbolt.Tx) error {
+		_, err := tx.CreateBucketIfNotExists(authPoliciesIndex)
+		return err
+	})
+	if err != nil {
+		_ = db.Close()
+		return nil, err
+	}
 
 	return h, nil
 }
@@ -99,12 +120,207 @@ func (h *MetadataHandler) Close() error {
 	return h.db.Close()
 }
 
+func (h *MetadataHandler) view(fn func(tx *bbolt.Tx) error) error {
+	start := time.Now()
+	err := h.db.View(fn)
+	metrics.Default.ObserveMetadataTx("view", time.Since(start), err == nil)
+	return err
+}
+
+func (h *MetadataHandler) update(fn func(tx *bbolt.Tx) error) error {
+	start := time.Now()
+	err := h.db.Update(fn)
+	metrics.Default.ObserveMetadataTx("update", time.Since(start), err == nil)
+	return err
+}
+
+func (h *MetadataHandler) PutAuthIdentity(identity *models.AuthIdentity) error {
+	if identity == nil {
+		return errors.New("auth identity is required")
+	}
+	if strings.TrimSpace(identity.AccessKeyID) == "" {
+		return errors.New("access key id is required")
+	}
+	return h.update(func(tx *bbolt.Tx) error {
+		bucket := tx.Bucket(authIdentitiesIndex)
+		if bucket == nil {
+			return errors.New("auth identities index not found")
+		}
+		payload, err := json.Marshal(identity)
+		if err != nil {
+			return err
+		}
+		return bucket.Put([]byte(identity.AccessKeyID), payload)
+	})
+}
+
+func (h *MetadataHandler) DeleteAuthIdentity(accessKeyID string) error {
+	accessKeyID = strings.TrimSpace(accessKeyID)
+	if accessKeyID == "" {
+		return errors.New("access key id is required")
+	}
+	return h.update(func(tx *bbolt.Tx) error {
+		bucket := tx.Bucket(authIdentitiesIndex)
+		if bucket == nil {
+			return errors.New("auth identities index not found")
+		}
+		if bucket.Get([]byte(accessKeyID)) == nil {
+			return fmt.Errorf("%w: %s", ErrAuthIdentityNotFound, accessKeyID)
+		}
+		return bucket.Delete([]byte(accessKeyID))
+	})
+}
+
+func (h *MetadataHandler) GetAuthIdentity(accessKeyID string) (*models.AuthIdentity, error) {
+	accessKeyID = strings.TrimSpace(accessKeyID)
+	if accessKeyID == "" {
+		return nil, errors.New("access key id is required")
+	}
+
+	var identity *models.AuthIdentity
+	err := h.view(func(tx *bbolt.Tx) error {
+		bucket := tx.Bucket(authIdentitiesIndex)
+		if bucket == nil {
+			return errors.New("auth identities index not found")
+		}
+		payload := bucket.Get([]byte(accessKeyID))
+		if payload == nil {
+			return fmt.Errorf("%w: %s", ErrAuthIdentityNotFound, accessKeyID)
+		}
+		record := models.AuthIdentity{}
+		if err := json.Unmarshal(payload, &record); err != nil {
+			return err
+		}
+		identity = &record
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return identity, nil
+}
+
+func (h *MetadataHandler) PutAuthPolicy(policy *models.AuthPolicy) error {
+	if policy == nil {
+		return errors.New("auth policy is required")
+	}
+	principal := strings.TrimSpace(policy.Principal)
+	if principal == "" {
+		return errors.New("auth policy principal is required")
+	}
+	policy.Principal = principal
+	return h.update(func(tx *bbolt.Tx) error {
+		bucket := tx.Bucket(authPoliciesIndex)
+		if bucket == nil {
+			return errors.New("auth policies index not found")
+		}
+		payload, err := json.Marshal(policy)
+		if err != nil {
+			return err
+		}
+		return bucket.Put([]byte(principal), payload)
+	})
+}
+
+func (h *MetadataHandler) DeleteAuthPolicy(accessKeyID string) error {
+	accessKeyID = strings.TrimSpace(accessKeyID)
+	if accessKeyID == "" {
+		return errors.New("access key id is required")
+	}
+	return h.update(func(tx *bbolt.Tx) error {
+		bucket := tx.Bucket(authPoliciesIndex)
+		if bucket == nil {
+			return errors.New("auth policies index not found")
+		}
+		if bucket.Get([]byte(accessKeyID)) == nil {
+			return fmt.Errorf("%w: %s", ErrAuthPolicyNotFound, accessKeyID)
+		}
+		return bucket.Delete([]byte(accessKeyID))
+	})
+}
+
+func (h *MetadataHandler) GetAuthPolicy(accessKeyID string) (*models.AuthPolicy, error) {
+	accessKeyID = strings.TrimSpace(accessKeyID)
+	if accessKeyID == "" {
+		return nil, errors.New("access key id is required")
+	}
+
+	var policy *models.AuthPolicy
+	err := h.view(func(tx *bbolt.Tx) error {
+		bucket := tx.Bucket(authPoliciesIndex)
+		if bucket == nil {
+			return errors.New("auth policies index not found")
+		}
+		payload := bucket.Get([]byte(accessKeyID))
+		if payload == nil {
+			return fmt.Errorf("%w: %s", ErrAuthPolicyNotFound, accessKeyID)
+		}
+		record := models.AuthPolicy{}
+		if err := json.Unmarshal(payload, &record); err != nil {
+			return err
+		}
+		policy = &record
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return policy, nil
+}
+
+func (h *MetadataHandler) ListAuthIdentities(limit int, after string) ([]models.AuthIdentity, string, error) {
+	if limit <= 0 {
+		limit = 100
+	}
+	after = strings.TrimSpace(after)
+
+	identities := make([]models.AuthIdentity, 0, limit)
+	nextCursor := ""
+
+	err := h.view(func(tx *bbolt.Tx) error {
+		bucket := tx.Bucket(authIdentitiesIndex)
+		if bucket == nil {
+			return errors.New("auth identities index not found")
+		}
+
+		cursor := bucket.Cursor()
+		var k, v []byte
+		if after == "" {
+			k, v = cursor.First()
+		} else {
+			k, v = cursor.Seek([]byte(after))
+			if k != nil && string(k) == after {
+				k, v = cursor.Next()
+			}
+		}
+
+		count := 0
+		for ; k != nil; k, v = cursor.Next() {
+			if count >= limit {
+				nextCursor = string(k)
+				break
+			}
+			record := models.AuthIdentity{}
+			if err := json.Unmarshal(v, &record); err != nil {
+				return err
+			}
+			identities = append(identities, record)
+			count++
+		}
+		return nil
+	})
+	if err != nil {
+		return nil, "", err
+	}
+	return identities, nextCursor, nil
+}
+
 func (h *MetadataHandler) CreateBucket(bucketName string) error {
 	if !isValidBucketName(bucketName) {
 		return fmt.Errorf("%w: %s", ErrInvalidBucketName, bucketName)
 	}
 
-	err := h.db.Update(func(tx *bbolt.Tx) error {
+	err := h.update(func(tx *bbolt.Tx) error {
 		indexBucket, err := tx.CreateBucketIfNotExists([]byte(systemIndex))
 		if err != nil {
 			return err
@@ -136,7 +352,7 @@ func (h *MetadataHandler) DeleteBucket(bucketName string) error {
 		return fmt.Errorf("%w: %s", ErrInvalidBucketName, bucketName)
 	}
 
-	err := h.db.Update(func(tx *bbolt.Tx) error {
+	err := h.update(func(tx *bbolt.Tx) error {
 		indexBucket, err := tx.CreateBucketIfNotExists([]byte(systemIndex))
 		if err != nil {
 			return err
@@ -183,7 +399,7 @@ func (h *MetadataHandler) DeleteBucket(bucketName string) error {
 
 func (h *MetadataHandler) ListBuckets() ([]string, error) {
 	buckets := []string{}
-	err := h.db.View(func(tx *bbolt.Tx) error {
+	err := h.view(func(tx *bbolt.Tx) error {
 		systemIndexBucket := tx.Bucket([]byte(systemIndex))
 		if systemIndexBucket == nil {
 			return errors.New("system index not found")
@@ -203,7 +419,7 @@ func (h *MetadataHandler) ListBuckets() ([]string, error) {
 func (h *MetadataHandler) GetBucketManifest(bucketName string) (*models.BucketManifest, error) {
 	var manifest *models.BucketManifest
 
-	err := h.db.View(func(tx *bbolt.Tx) error {
+	err := h.view(func(tx *bbolt.Tx) error {
 		systemIndexBucket := tx.Bucket([]byte(systemIndex))
 		if systemIndexBucket == nil {
 			return errors.New("system index not found")
@@ -233,7 +449,7 @@ func (h *MetadataHandler) PutManifest(manifest *models.ObjectManifest) error {
 		return err
 	}
 
-	err := h.db.Update(func(tx *bbolt.Tx) error {
+	err := h.update(func(tx *bbolt.Tx) error {
 		data, err := json.Marshal(manifest)
 		if err != nil {
 			return err
@@ -253,7 +469,7 @@ func (h *MetadataHandler) PutManifest(manifest *models.ObjectManifest) error {
 func (h *MetadataHandler) GetManifest(bucket, key string) (*models.ObjectManifest, error) {
 	var manifest *models.ObjectManifest
 
-	err := h.db.View(func(tx *bbolt.Tx) error {
+	err := h.view(func(tx *bbolt.Tx) error {
 		metadataBucket := tx.Bucket([]byte(bucket))
 		if metadataBucket == nil {
 			return fmt.Errorf("%w: %s", ErrBucketNotFound, bucket)
@@ -280,7 +496,7 @@ func (h *MetadataHandler) ListObjects(bucket, prefix string) ([]*models.ObjectMa
 
 	var objects []*models.ObjectManifest
 
-	err := h.db.View(func(tx *bbolt.Tx) error {
+	err := h.view(func(tx *bbolt.Tx) error {
 		systemIndexBucket := tx.Bucket([]byte(systemIndex))
 		if systemIndexBucket == nil {
 			return errors.New("system index not found")
@@ -320,7 +536,7 @@ func (h *MetadataHandler) ForEachObjectFrom(bucket, startKey string, fn func(*mo
 		return errors.New("object callback is required")
 	}
 
-	return h.db.View(func(tx *bbolt.Tx) error {
+	return h.view(func(tx *bbolt.Tx) error {
 		systemIndexBucket := tx.Bucket([]byte(systemIndex))
 		if systemIndexBucket == nil {
 			return errors.New("system index not found")
@@ -360,7 +576,7 @@ func (h *MetadataHandler) DeleteManifest(bucket, key string) error {
 		return err
 	}
 
-	err := h.db.Update(func(tx *bbolt.Tx) error {
+	err := h.update(func(tx *bbolt.Tx) error {
 		metadataBucket := tx.Bucket([]byte(bucket))
 		if metadataBucket == nil {
 			return fmt.Errorf("%w: %s", ErrBucketNotFound, bucket)
@@ -377,7 +593,7 @@ func (h *MetadataHandler) DeleteManifest(bucket, key string) error {
 func (h *MetadataHandler) DeleteManifests(bucket string, keys []string) ([]string, error) {
 	deleted := make([]string, 0, len(keys))
 
-	err := h.db.Update(func(tx *bbolt.Tx) error {
+	err := h.update(func(tx *bbolt.Tx) error {
 		metadataBucket := tx.Bucket([]byte(bucket))
 		if metadataBucket == nil {
 			return fmt.Errorf("%w: %s", ErrBucketNotFound, bucket)
@@ -405,7 +621,7 @@ func (h *MetadataHandler) DeleteManifests(bucket string, keys []string) ([]strin
 func (h *MetadataHandler) CreateMultipartUpload(bucket, key string) (*models.MultipartUpload, error) {
 	var upload *models.MultipartUpload
 
-	err := h.db.View(func(tx *bbolt.Tx) error {
+	err := h.view(func(tx *bbolt.Tx) error {
 		systemIndexBucket := tx.Bucket([]byte(systemIndex))
 		if systemIndexBucket == nil {
 			return errors.New("system index not found")
@@ -428,7 +644,7 @@ func (h *MetadataHandler) CreateMultipartUpload(bucket, key string) (*models.Mul
 		State:     "pending",
 	}
 
-	err = h.db.Update(func(tx *bbolt.Tx) error {
+	err = h.update(func(tx *bbolt.Tx) error {
 		multipartUploadBucket := tx.Bucket([]byte(multipartUploadIndex))
 		if multipartUploadBucket == nil {
 			return errors.New("multipart upload index not found")
@@ -523,7 +739,7 @@ func deleteMultipartPartsByUploadID(tx *bbolt.Tx, uploadID string) error {
 
 func (h *MetadataHandler) GetMultipartUpload(uploadID string) (*models.MultipartUpload, error) {
 	var upload *models.MultipartUpload
-	err := h.db.View(func(tx *bbolt.Tx) error {
+	err := h.view(func(tx *bbolt.Tx) error {
 		var err error
 		upload, _, err = getMultipartUploadFromTx(tx, uploadID)
 		if err != nil {
@@ -541,7 +757,7 @@ func (h *MetadataHandler) PutMultipartPart(uploadID string, part models.Uploaded
 		return fmt.Errorf("invalid part number: %d", part.PartNumber)
 	}
 
-	err := h.db.Update(func(tx *bbolt.Tx) error {
+	err := h.update(func(tx *bbolt.Tx) error {
 		upload, _, err := getMultipartUploadFromTx(tx, uploadID)
 		if err != nil {
 			return err
@@ -570,7 +786,7 @@ func (h *MetadataHandler) PutMultipartPart(uploadID string, part models.Uploaded
 func (h *MetadataHandler) ListMultipartParts(uploadID string) ([]models.UploadedPart, error) {
 	parts := make([]models.UploadedPart, 0)
 
-	err := h.db.View(func(tx *bbolt.Tx) error {
+	err := h.view(func(tx *bbolt.Tx) error {
 		if _, _, err := getMultipartUploadFromTx(tx, uploadID); err != nil {
 			return err
 		}
@@ -604,7 +820,7 @@ func (h *MetadataHandler) CompleteMultipartUpload(uploadID string, final *models
 		return errors.New("final object manifest is required")
 	}
 
-	err := h.db.Update(func(tx *bbolt.Tx) error {
+	err := h.update(func(tx *bbolt.Tx) error {
 		upload, multipartUploadBucket, err := getMultipartUploadFromTx(tx, uploadID)
 		if err != nil {
 			return err
@@ -643,7 +859,7 @@ func (h *MetadataHandler) CompleteMultipartUpload(uploadID string, final *models
 	return nil
 }
 func (h *MetadataHandler) AbortMultipartUpload(uploadID string) error {
-	err := h.db.Update(func(tx *bbolt.Tx) error {
+	err := h.update(func(tx *bbolt.Tx) error {
 		upload, multipartUploadBucket, err := getMultipartUploadFromTx(tx, uploadID)
 		if err != nil {
 			return err
@@ -673,7 +889,7 @@ func (h *MetadataHandler) CleanupMultipartUploads(retention time.Duration) (int,
 	}
 
 	cleaned := 0
-	err := h.db.Update(func(tx *bbolt.Tx) error {
+	err := h.update(func(tx *bbolt.Tx) error {
 		uploadsBucket, err := getMultipartUploadBucket(tx)
 		if err != nil {
 			return err
@@ -723,7 +939,7 @@ func (h *MetadataHandler) GetReferencedChunkSet() (map[string]struct{}, error) {
 	chunkSet := make(map[string]struct{})
 	pendingUploadSet := make(map[string]struct{})
 
-	err := h.db.View(func(tx *bbolt.Tx) error {
+	err := h.view(func(tx *bbolt.Tx) error {
 		systemIndexBucket := tx.Bucket([]byte(systemIndex))
 		if systemIndexBucket == nil {
 			return errors.New("system index not found")

metrics/metrics.go

@@ -0,0 +1,795 @@
+package metrics
+
+import (
+	"fmt"
+	"os"
+	"runtime"
+	"sort"
+	"strconv"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"syscall"
+	"time"
+)
+
+var defaultBuckets = []float64{
+	0.0005, 0.001, 0.0025, 0.005, 0.01,
+	0.025, 0.05, 0.1, 0.25, 0.5,
+	1, 2.5, 5, 10,
+}
+
+var lockBuckets = []float64{
+	0.000001, 0.000005, 0.00001, 0.00005,
+	0.0001, 0.0005, 0.001, 0.005, 0.01,
+	0.025, 0.05, 0.1, 0.25, 0.5, 1,
+}
+
+var batchBuckets = []float64{1, 2, 4, 8, 16, 32, 64, 100, 128, 256, 512, 1000, 5000}
+
+var Default = NewRegistry()
+
+type histogram struct {
+	bounds []float64
+	counts []uint64
+	sum    float64
+	count  uint64
+}
+
+func newHistogram(bounds []float64) *histogram {
+	cloned := make([]float64, len(bounds))
+	copy(cloned, bounds)
+	return &histogram{
+		bounds: cloned,
+		counts: make([]uint64, len(bounds)+1),
+	}
+}
+
+func (h *histogram) observe(v float64) {
+	h.count++
+	h.sum += v
+	for i, bound := range h.bounds {
+		if v <= bound {
+			h.counts[i]++
+			return
+		}
+	}
+	h.counts[len(h.counts)-1]++
+}
+
+func (h *histogram) snapshot() (bounds []float64, counts []uint64, sum float64, count uint64) {
+	bounds = make([]float64, len(h.bounds))
+	copy(bounds, h.bounds)
+	counts = make([]uint64, len(h.counts))
+	copy(counts, h.counts)
+	return bounds, counts, h.sum, h.count
+}
+
+type Registry struct {
+	startedAt time.Time
+
+	httpInFlight atomic.Int64
+
+	connectionPoolActive atomic.Int64
+	connectionPoolMax    atomic.Int64
+	connectionPoolWaits  atomic.Uint64
+
+	requestQueueLength atomic.Int64
+
+	mu sync.Mutex
+
+	httpRequestsRoute      map[string]uint64
+	httpResponseBytesRoute map[string]uint64
+	httpDurationRoute      map[string]*histogram
+
+	httpRequestsOp map[string]uint64
+	httpDurationOp map[string]*histogram
+	httpInFlightOp map[string]int64
+
+	authRequests map[string]uint64
+
+	serviceOps      map[string]uint64
+	serviceDuration map[string]*histogram
+
+	dbTxTotal    map[string]uint64
+	dbTxDuration map[string]*histogram
+
+	blobOps      map[string]uint64
+	blobBytes    map[string]uint64
+	blobDuration map[string]*histogram
+
+	lockWait map[string]*histogram
+	lockHold map[string]*histogram
+
+	cacheHits   map[string]uint64
+	cacheMisses map[string]uint64
+
+	batchSize *histogram
+
+	retries map[string]uint64
+	errors  map[string]uint64
+
+	gcRuns          map[string]uint64
+	gcDuration      *histogram
+	gcDeletedChunks uint64
+	gcDeleteErrors  uint64
+	gcCleanedUpload uint64
+}
+
+func NewRegistry() *Registry {
+	return &Registry{
+		startedAt:              time.Now(),
+		httpRequestsRoute:      make(map[string]uint64),
+		httpResponseBytesRoute: make(map[string]uint64),
+		httpDurationRoute:      make(map[string]*histogram),
+		httpRequestsOp:         make(map[string]uint64),
+		httpDurationOp:         make(map[string]*histogram),
+		httpInFlightOp:         make(map[string]int64),
+		authRequests:           make(map[string]uint64),
+		serviceOps:             make(map[string]uint64),
+		serviceDuration:        make(map[string]*histogram),
+		dbTxTotal:              make(map[string]uint64),
+		dbTxDuration:           make(map[string]*histogram),
+		blobOps:                make(map[string]uint64),
+		blobBytes:              make(map[string]uint64),
+		blobDuration:           make(map[string]*histogram),
+		lockWait:               make(map[string]*histogram),
+		lockHold:               make(map[string]*histogram),
+		cacheHits:              make(map[string]uint64),
+		cacheMisses:            make(map[string]uint64),
+		batchSize:              newHistogram(batchBuckets),
+		retries:                make(map[string]uint64),
+		errors:                 make(map[string]uint64),
+		gcRuns:                 make(map[string]uint64),
+		gcDuration:             newHistogram(defaultBuckets),
+	}
+}
+
+func NormalizeHTTPOperation(method string, isDeletePost bool) string {
+	switch strings.ToUpper(strings.TrimSpace(method)) {
+	case "GET":
+		return "get"
+	case "PUT":
+		return "put"
+	case "DELETE":
+		return "delete"
+	case "HEAD":
+		return "head"
+	case "POST":
+		if isDeletePost {
+			return "delete"
+		}
+		return "put"
+	default:
+		return "other"
+	}
+}
+
+func statusResult(status int) string {
+	if status >= 200 && status < 400 {
+		return "ok"
+	}
+	return "error"
+}
+
+func normalizeRoute(route string) string {
+	route = strings.TrimSpace(route)
+	if route == "" {
+		return "/unknown"
+	}
+	return route
+}
+
+func normalizeOp(op string) string {
+	op = strings.ToLower(strings.TrimSpace(op))
+	if op == "" {
+		return "other"
+	}
+	return op
+}
+
+func (r *Registry) IncHTTPInFlight() {
+	r.httpInFlight.Add(1)
+}
+
+func (r *Registry) DecHTTPInFlight() {
+	r.httpInFlight.Add(-1)
+}
+
+func (r *Registry) IncHTTPInFlightOp(op string) {
+	r.httpInFlight.Add(1)
+	op = normalizeOp(op)
+	r.mu.Lock()
+	r.httpInFlightOp[op]++
+	r.mu.Unlock()
+}
+
+func (r *Registry) DecHTTPInFlightOp(op string) {
+	r.httpInFlight.Add(-1)
+	op = normalizeOp(op)
+	r.mu.Lock()
+	r.httpInFlightOp[op]--
+	if r.httpInFlightOp[op] < 0 {
+		r.httpInFlightOp[op] = 0
+	}
+	r.mu.Unlock()
+}
+
+func (r *Registry) ObserveHTTPRequest(method, route string, status int, d time.Duration, responseBytes int) {
+	op := NormalizeHTTPOperation(method, false)
+	r.ObserveHTTPRequestDetailed(method, route, op, status, d, responseBytes)
+}
+
+func (r *Registry) ObserveHTTPRequestDetailed(method, route, op string, status int, d time.Duration, responseBytes int) {
+	route = normalizeRoute(route)
+	op = normalizeOp(op)
+	result := statusResult(status)
+
+	routeKey := method + "|" + route + "|" + strconv.Itoa(status)
+	routeDurKey := method + "|" + route
+	opKey := op + "|" + result
+
+	r.mu.Lock()
+	r.httpRequestsRoute[routeKey]++
+	if responseBytes > 0 {
+		r.httpResponseBytesRoute[routeKey] += uint64(responseBytes)
+	}
+	hRoute := r.httpDurationRoute[routeDurKey]
+	if hRoute == nil {
+		hRoute = newHistogram(defaultBuckets)
+		r.httpDurationRoute[routeDurKey] = hRoute
+	}
+	hRoute.observe(d.Seconds())
+
+	r.httpRequestsOp[opKey]++
+	hOp := r.httpDurationOp[opKey]
+	if hOp == nil {
+		hOp = newHistogram(defaultBuckets)
+		r.httpDurationOp[opKey] = hOp
+	}
+	hOp.observe(d.Seconds())
+	r.mu.Unlock()
+}
+
+func (r *Registry) ObserveAuth(result, authType, reason string) {
+	authType = strings.TrimSpace(authType)
+	if authType == "" {
+		authType = "unknown"
+	}
+	reason = strings.TrimSpace(reason)
+	if reason == "" {
+		reason = "none"
+	}
+	key := result + "|" + authType + "|" + reason
+	r.mu.Lock()
+	r.authRequests[key]++
+	r.mu.Unlock()
+}
+
+func (r *Registry) ObserveService(operation string, d time.Duration, ok bool) {
+	result := "error"
+	if ok {
+		result = "ok"
+	}
+	key := operation + "|" + result
+	r.mu.Lock()
+	r.serviceOps[key]++
+	h := r.serviceDuration[operation]
+	if h == nil {
+		h = newHistogram(defaultBuckets)
+		r.serviceDuration[operation] = h
+	}
+	h.observe(d.Seconds())
+	r.mu.Unlock()
+}
+
+func (r *Registry) ObserveMetadataTx(txType string, d time.Duration, ok bool) {
+	result := "error"
+	if ok {
+		result = "ok"
+	}
+	key := txType + "|" + result
+	r.mu.Lock()
+	r.dbTxTotal[key]++
+	h := r.dbTxDuration[txType]
+	if h == nil {
+		h = newHistogram(defaultBuckets)
+		r.dbTxDuration[txType] = h
+	}
+	h.observe(d.Seconds())
+	r.mu.Unlock()
+}
+
+func (r *Registry) ObserveBlob(operation string, d time.Duration, bytes int64, ok bool, backend ...string) {
+	be := "disk"
+	if len(backend) > 0 {
+		candidate := strings.TrimSpace(backend[0])
+		if candidate != "" {
+			be = strings.ToLower(candidate)
+		}
+	}
+	result := "error"
+	if ok {
+		result = "ok"
+	}
+	op := strings.ToLower(strings.TrimSpace(operation))
+	if op == "" {
+		op = "unknown"
+	}
+
+	histKey := op + "|" + be + "|" + result
+	opsKey := histKey
+
+	r.mu.Lock()
+	r.blobOps[opsKey]++
+	h := r.blobDuration[histKey]
+	if h == nil {
+		h = newHistogram(defaultBuckets)
+		r.blobDuration[histKey] = h
+	}
+	h.observe(d.Seconds())
+
+	if bytes > 0 {
+		r.blobBytes[op] += uint64(bytes)
+	}
+	r.mu.Unlock()
+}
+
+func (r *Registry) SetConnectionPoolMax(max int) {
+	if max < 0 {
+		max = 0
+	}
+	r.connectionPoolMax.Store(int64(max))
+}
+
+func (r *Registry) IncConnectionPoolActive() {
+	r.connectionPoolActive.Add(1)
+}
+
+func (r *Registry) DecConnectionPoolActive() {
+	r.connectionPoolActive.Add(-1)
+}
+
+func (r *Registry) IncConnectionPoolWait() {
+	r.connectionPoolWaits.Add(1)
+}
+
+func (r *Registry) IncRequestQueueLength() {
+	r.requestQueueLength.Add(1)
+}
+
+func (r *Registry) DecRequestQueueLength() {
+	r.requestQueueLength.Add(-1)
+}
+
+func (r *Registry) ObserveLockWait(lockName string, d time.Duration) {
+	lockName = strings.TrimSpace(lockName)
+	if lockName == "" {
+		lockName = "unknown"
+	}
+	r.mu.Lock()
+	h := r.lockWait[lockName]
+	if h == nil {
+		h = newHistogram(lockBuckets)
+		r.lockWait[lockName] = h
+	}
+	h.observe(d.Seconds())
+	r.mu.Unlock()
+}
+
+func (r *Registry) ObserveLockHold(lockName string, d time.Duration) {
+	lockName = strings.TrimSpace(lockName)
+	if lockName == "" {
+		lockName = "unknown"
+	}
+	r.mu.Lock()
+	h := r.lockHold[lockName]
+	if h == nil {
+		h = newHistogram(lockBuckets)
+		r.lockHold[lockName] = h
+	}
+	h.observe(d.Seconds())
+	r.mu.Unlock()
+}
+
+func (r *Registry) ObserveCacheHit(cache string) {
+	cache = strings.TrimSpace(cache)
+	if cache == "" {
+		cache = "unknown"
+	}
+	r.mu.Lock()
+	r.cacheHits[cache]++
+	r.mu.Unlock()
+}
+
+func (r *Registry) ObserveCacheMiss(cache string) {
+	cache = strings.TrimSpace(cache)
+	if cache == "" {
+		cache = "unknown"
+	}
+	r.mu.Lock()
+	r.cacheMisses[cache]++
+	r.mu.Unlock()
+}
+
+func (r *Registry) ObserveBatchSize(size int) {
+	if size < 0 {
+		size = 0
+	}
+	r.mu.Lock()
+	r.batchSize.observe(float64(size))
+	r.mu.Unlock()
+}
+
+func (r *Registry) ObserveRetry(op, reason string) {
+	op = normalizeOp(op)
+	reason = strings.TrimSpace(reason)
+	if reason == "" {
+		reason = "unknown"
+	}
+	key := op + "|" + reason
+	r.mu.Lock()
+	r.retries[key]++
+	r.mu.Unlock()
+}
+
+func (r *Registry) ObserveError(op, reason string) {
+	op = normalizeOp(op)
+	reason = strings.TrimSpace(reason)
+	if reason == "" {
+		reason = "unknown"
+	}
+	key := op + "|" + reason
+	r.mu.Lock()
+	r.errors[key]++
+	r.mu.Unlock()
+}
+
+func (r *Registry) ObserveGC(d time.Duration, deletedChunks, deleteErrors, cleanedUploads int, ok bool) {
+	result := "error"
+	if ok {
+		result = "ok"
+	}
+	r.mu.Lock()
+	r.gcRuns[result]++
+	r.gcDuration.observe(d.Seconds())
+	if deletedChunks > 0 {
+		r.gcDeletedChunks += uint64(deletedChunks)
+	}
+	if deleteErrors > 0 {
+		r.gcDeleteErrors += uint64(deleteErrors)
+	}
+	if cleanedUploads > 0 {
+		r.gcCleanedUpload += uint64(cleanedUploads)
+	}
+	r.mu.Unlock()
+}
+
+func (r *Registry) RenderPrometheus() string {
+	now := time.Now()
+	var mem runtime.MemStats
+	runtime.ReadMemStats(&mem)
+
+	r.mu.Lock()
+	httpReqRoute := copyCounterMap(r.httpRequestsRoute)
+	httpRespRoute := copyCounterMap(r.httpResponseBytesRoute)
+	httpDurRoute := copyHistogramMap(r.httpDurationRoute)
+	httpReqOp := copyCounterMap(r.httpRequestsOp)
+	httpDurOp := copyHistogramMap(r.httpDurationOp)
+	httpInFlightOp := copyIntGaugeMap(r.httpInFlightOp)
+	authReq := copyCounterMap(r.authRequests)
+	serviceOps := copyCounterMap(r.serviceOps)
+	serviceDur := copyHistogramMap(r.serviceDuration)
+	dbTx := copyCounterMap(r.dbTxTotal)
+	dbTxDur := copyHistogramMap(r.dbTxDuration)
+	blobOps := copyCounterMap(r.blobOps)
+	blobBytes := copyCounterMap(r.blobBytes)
+	blobDur := copyHistogramMap(r.blobDuration)
+	lockWait := copyHistogramMap(r.lockWait)
+	lockHold := copyHistogramMap(r.lockHold)
+	cacheHits := copyCounterMap(r.cacheHits)
+	cacheMisses := copyCounterMap(r.cacheMisses)
+	batchBounds, batchCounts, batchSum, batchCount := r.batchSize.snapshot()
+	retries := copyCounterMap(r.retries)
+	errorsTotal := copyCounterMap(r.errors)
+	gcRuns := copyCounterMap(r.gcRuns)
+	gcDurBounds, gcDurCounts, gcDurSum, gcDurCount := r.gcDuration.snapshot()
+	gcDeletedChunks := r.gcDeletedChunks
+	gcDeleteErrors := r.gcDeleteErrors
+	gcCleanedUploads := r.gcCleanedUpload
+	r.mu.Unlock()
+
+	connectionActive := float64(r.connectionPoolActive.Load())
+	connectionMax := float64(r.connectionPoolMax.Load())
+	connectionWaits := r.connectionPoolWaits.Load()
+	queueLength := float64(r.requestQueueLength.Load())
+
+	resident, hasResident := readResidentMemoryBytes()
+	cpuSeconds, hasCPU := readProcessCPUSeconds()
+
+	var b strings.Builder
+
+	httpInFlightOp["all"] = r.httpInFlight.Load()
+	writeGaugeVecFromInt64(&b, "fs_http_inflight_requests", "Current in-flight HTTP requests by operation.", httpInFlightOp, "op")
+	writeCounterVecKV(&b, "fs_http_requests_total", "Total HTTP requests by operation and result.", httpReqOp, []string{"op", "result"})
+	writeHistogramVecKV(&b, "fs_http_request_duration_seconds", "HTTP request latency by operation and result.", httpDurOp, []string{"op", "result"})
+
+	writeCounterVecKV(&b, "fs_http_requests_by_route_total", "Total HTTP requests by method/route/status.", httpReqRoute, []string{"method", "route", "status"})
+	writeCounterVecKV(&b, "fs_http_response_bytes_total", "Total HTTP response bytes written.", httpRespRoute, []string{"method", "route", "status"})
+	writeHistogramVecKV(&b, "fs_http_request_duration_by_route_seconds", "HTTP request latency by method/route.", httpDurRoute, []string{"method", "route"})
+
+	writeCounterVecKV(&b, "fs_auth_requests_total", "Authentication attempts by result.", authReq, []string{"result", "auth_type", "reason"})
+
+	writeCounterVecKV(&b, "fs_service_operations_total", "Service-level operation calls.", serviceOps, []string{"operation", "result"})
+	writeHistogramVecKV(&b, "fs_service_operation_duration_seconds", "Service-level operation latency.", serviceDur, []string{"operation"})
+
+	writeCounterVecKV(&b, "fs_metadata_tx_total", "Metadata transaction calls.", dbTx, []string{"type", "result"})
+	writeHistogramVecKV(&b, "fs_metadata_tx_duration_seconds", "Metadata transaction latency.", dbTxDur, []string{"type"})
+
+	writeHistogramVecKV(&b, "fs_blob_operation_duration_seconds", "Blob backend operation latency.", blobDur, []string{"op", "backend", "result"})
+	writeCounterVecKV(&b, "fs_blob_operations_total", "Blob store operations.", blobOps, []string{"op", "backend", "result"})
+	writeCounterVecKV(&b, "fs_blob_bytes_total", "Blob bytes processed by operation.", blobBytes, []string{"op"})
+
+	writeGauge(&b, "fs_connection_pool_active", "Active pooled connections.", connectionActive)
+	writeGauge(&b, "fs_connection_pool_max", "Maximum pooled connections.", connectionMax)
+	writeCounter(&b, "fs_connection_pool_waits_total", "Number of waits due to pool saturation.", connectionWaits)
+
+	writeGauge(&b, "fs_request_queue_length", "Requests waiting for an execution slot.", queueLength)
+
+	writeHistogramVecKV(&b, "fs_lock_wait_seconds", "Time spent waiting for locks.", lockWait, []string{"lock_name"})
+	writeHistogramVecKV(&b, "fs_lock_hold_seconds", "Time locks were held.", lockHold, []string{"lock_name"})
+
+	writeCounterVecKV(&b, "fs_cache_hits_total", "Cache hits by cache name.", cacheHits, []string{"cache"})
+	writeCounterVecKV(&b, "fs_cache_misses_total", "Cache misses by cache name.", cacheMisses, []string{"cache"})
+
+	writeHistogram(&b, "fs_batch_size_histogram", "Observed batch sizes.", nil, batchBounds, batchCounts, batchSum, batchCount)
+
+	writeCounterVecKV(&b, "fs_retries_total", "Retries by operation and reason.", retries, []string{"op", "reason"})
+	writeCounterVecKV(&b, "fs_errors_total", "Errors by operation and reason.", errorsTotal, []string{"op", "reason"})
+
+	writeCounterVecKV(&b, "fs_gc_runs_total", "Garbage collection runs.", gcRuns, []string{"result"})
+	writeHistogram(&b, "fs_gc_duration_seconds", "Garbage collection runtime.", nil, gcDurBounds, gcDurCounts, gcDurSum, gcDurCount)
+	writeCounter(&b, "fs_gc_deleted_chunks_total", "Deleted chunks during GC.", gcDeletedChunks)
+	writeCounter(&b, "fs_gc_delete_errors_total", "Chunk delete errors during GC.", gcDeleteErrors)
+	writeCounter(&b, "fs_gc_cleaned_uploads_total", "Cleaned multipart uploads during GC.", gcCleanedUploads)
+
+	writeGauge(&b, "fs_uptime_seconds", "Process uptime in seconds.", now.Sub(r.startedAt).Seconds())
+	writeGauge(&b, "fs_runtime_goroutines", "Number of goroutines.", float64(runtime.NumGoroutine()))
+	writeGaugeVec(&b, "fs_runtime_memory_bytes", "Runtime memory in bytes.", map[string]float64{
+		"alloc":      float64(mem.Alloc),
+		"total":      float64(mem.TotalAlloc),
+		"sys":        float64(mem.Sys),
+		"heap_alloc": float64(mem.HeapAlloc),
+		"heap_sys":   float64(mem.HeapSys),
+		"stack_sys":  float64(mem.StackSys),
+	}, "type")
+	writeCounter(&b, "fs_runtime_gc_cycles_total", "Completed GC cycles.", uint64(mem.NumGC))
+	writeCounterFloat(&b, "fs_runtime_gc_pause_seconds_total", "Total GC pause time in seconds.", float64(mem.PauseTotalNs)/1e9)
+
+	if hasCPU {
+		writeCounterFloat(&b, "process_cpu_seconds_total", "Total user and system CPU time spent in seconds.", cpuSeconds)
+	}
+	if hasResident {
+		writeGauge(&b, "process_resident_memory_bytes", "Resident memory size in bytes.", resident)
+	}
+
+	return b.String()
+}
+
+type histogramSnapshot struct {
+	bounds []float64
+	counts []uint64
+	sum    float64
+	count  uint64
+}
+
+func copyCounterMap(src map[string]uint64) map[string]uint64 {
+	out := make(map[string]uint64, len(src))
+	for k, v := range src {
+		out[k] = v
+	}
+	return out
+}
+
+func copyIntGaugeMap(src map[string]int64) map[string]int64 {
+	out := make(map[string]int64, len(src))
+	for k, v := range src {
+		out[k] = v
+	}
+	return out
+}
+
+func copyHistogramMap(src map[string]*histogram) map[string]histogramSnapshot {
+	out := make(map[string]histogramSnapshot, len(src))
+	for k, h := range src {
+		bounds, counts, sum, count := h.snapshot()
+		out[k] = histogramSnapshot{bounds: bounds, counts: counts, sum: sum, count: count}
+	}
+	return out
+}
+
+func writeCounter(b *strings.Builder, name, help string, value uint64) {
+	fmt.Fprintf(b, "# HELP %s %s\n", name, help)
+	fmt.Fprintf(b, "# TYPE %s counter\n", name)
+	fmt.Fprintf(b, "%s %d\n", name, value)
+}
+
+func writeCounterFloat(b *strings.Builder, name, help string, value float64) {
+	fmt.Fprintf(b, "# HELP %s %s\n", name, help)
+	fmt.Fprintf(b, "# TYPE %s counter\n", name)
+	fmt.Fprintf(b, "%s %.9f\n", name, value)
+}
+
+func writeGauge(b *strings.Builder, name, help string, value float64) {
+	fmt.Fprintf(b, "# HELP %s %s\n", name, help)
+	fmt.Fprintf(b, "# TYPE %s gauge\n", name)
+	fmt.Fprintf(b, "%s %.9f\n", name, value)
+}
+
+func writeGaugeVec(b *strings.Builder, name, help string, values map[string]float64, labelName string) {
+	fmt.Fprintf(b, "# HELP %s %s\n", name, help)
+	fmt.Fprintf(b, "# TYPE %s gauge\n", name)
+	keys := make([]string, 0, len(values))
+	for k := range values {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	for _, key := range keys {
+		fmt.Fprintf(b, "%s{%s=\"%s\"} %.9f\n", name, labelName, escapeLabelValue(key), values[key])
+	}
+}
+
+func writeGaugeVecFromInt64(b *strings.Builder, name, help string, values map[string]int64, labelName string) {
+	fmt.Fprintf(b, "# HELP %s %s\n", name, help)
+	fmt.Fprintf(b, "# TYPE %s gauge\n", name)
+	keys := make([]string, 0, len(values))
+	for k := range values {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	for _, key := range keys {
+		fmt.Fprintf(b, "%s{%s=\"%s\"} %.9f\n", name, labelName, escapeLabelValue(key), float64(values[key]))
+	}
+}
+
+func writeCounterVecKV(b *strings.Builder, name, help string, values map[string]uint64, labels []string) {
+	fmt.Fprintf(b, "# HELP %s %s\n", name, help)
+	fmt.Fprintf(b, "# TYPE %s counter\n", name)
+	keys := make([]string, 0, len(values))
+	for k := range values {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	for _, key := range keys {
+		parts := strings.Split(key, "|")
+		fmt.Fprintf(b, "%s{%s} %d\n", name, formatLabels(labels, parts), values[key])
+	}
+}
+
+func writeHistogramVecKV(b *strings.Builder, name, help string, values map[string]histogramSnapshot, labels []string) {
+	fmt.Fprintf(b, "# HELP %s %s\n", name, help)
+	fmt.Fprintf(b, "# TYPE %s histogram\n", name)
+	keys := make([]string, 0, len(values))
+	for k := range values {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	for _, key := range keys {
+		parts := strings.Split(key, "|")
+		labelsMap := make(map[string]string, len(labels))
+		for i, label := range labels {
+			if i < len(parts) {
+				labelsMap[label] = parts[i]
+			} else {
+				labelsMap[label] = ""
+			}
+		}
+		writeHistogramWithLabelsMap(b, name, labelsMap, values[key])
+	}
+}
+
+func writeHistogram(b *strings.Builder, name, help string, labels map[string]string, bounds []float64, counts []uint64, sum float64, count uint64) {
+	fmt.Fprintf(b, "# HELP %s %s\n", name, help)
+	fmt.Fprintf(b, "# TYPE %s histogram\n", name)
+	writeHistogramWithLabelsMap(b, name, labels, histogramSnapshot{bounds: bounds, counts: counts, sum: sum, count: count})
+}
+
+func writeHistogramWithLabelsMap(b *strings.Builder, name string, labels map[string]string, s histogramSnapshot) {
+	var cumulative uint64
+	for i, bucketCount := range s.counts {
+		cumulative += bucketCount
+		bucketLabels := cloneLabels(labels)
+		if i < len(s.bounds) {
+			bucketLabels["le"] = trimFloat(s.bounds[i])
+		} else {
+			bucketLabels["le"] = "+Inf"
+		}
+		fmt.Fprintf(b, "%s_bucket{%s} %d\n", name, labelsToString(bucketLabels), cumulative)
+	}
+	labelsSuffix := formatLabelsSuffix(labels)
+	fmt.Fprintf(b, "%s_sum%s %.9f\n", name, labelsSuffix, s.sum)
+	fmt.Fprintf(b, "%s_count%s %d\n", name, labelsSuffix, s.count)
+}
+
+func formatLabelsSuffix(labels map[string]string) string {
+	if len(labels) == 0 {
+		return ""
+	}
+	return "{" + labelsToString(labels) + "}"
+}
+
+func formatLabels(keys, values []string) string {
+	parts := make([]string, 0, len(keys))
+	for i, key := range keys {
+		value := ""
+		if i < len(values) {
+			value = values[i]
+		}
+		parts = append(parts, fmt.Sprintf("%s=\"%s\"", key, escapeLabelValue(value)))
+	}
+	return strings.Join(parts, ",")
+}
+
+func labelsToString(labels map[string]string) string {
+	if len(labels) == 0 {
+		return ""
+	}
+	keys := make([]string, 0, len(labels))
+	for k := range labels {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	parts := make([]string, 0, len(keys))
+	for _, key := range keys {
+		parts = append(parts, fmt.Sprintf("%s=\"%s\"", key, escapeLabelValue(labels[key])))
+	}
+	return strings.Join(parts, ",")
+}
+
+func cloneLabels(in map[string]string) map[string]string {
+	if len(in) == 0 {
+		return map[string]string{}
+	}
+	out := make(map[string]string, len(in)+1)
+	for k, v := range in {
+		out[k] = v
+	}
+	return out
+}
+
+func trimFloat(v float64) string {
+	return strconv.FormatFloat(v, 'f', -1, 64)
+}
+
+func escapeLabelValue(value string) string {
+	value = strings.ReplaceAll(value, `\`, `\\`)
+	value = strings.ReplaceAll(value, "\n", `\n`)
+	value = strings.ReplaceAll(value, `"`, `\"`)
+	return value
+}
+
+func readResidentMemoryBytes() (float64, bool) {
+	data, err := os.ReadFile("/proc/self/statm")
+	if err != nil {
+		return 0, false
+	}
+	fields := strings.Fields(string(data))
+	if len(fields) < 2 {
+		return 0, false
+	}
+	rssPages, err := strconv.ParseInt(fields[1], 10, 64)
+	if err != nil || rssPages < 0 {
+		return 0, false
+	}
+	return float64(rssPages * int64(os.Getpagesize())), true
+}
+
+func readProcessCPUSeconds() (float64, bool) {
+	var usage syscall.Rusage
+	if err := syscall.Getrusage(syscall.RUSAGE_SELF, &usage); err != nil {
+		return 0, false
+	}
+	user := float64(usage.Utime.Sec) + float64(usage.Utime.Usec)/1e6
+	sys := float64(usage.Stime.Sec) + float64(usage.Stime.Usec)/1e6
+	return user + sys, true
+}

metrics/metrics_test.go

@@ -0,0 +1,34 @@
+package metrics
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestRenderPrometheusHistogramNoEmptyLabelSet(t *testing.T) {
+	reg := NewRegistry()
+	reg.ObserveBatchSize(3)
+	reg.ObserveGC(0, 0, 0, 0, true)
+
+	out := reg.RenderPrometheus()
+	if strings.Contains(out, "fs_batch_size_histogram_sum{}") {
+		t.Fatalf("unexpected empty label set for batch sum metric")
+	}
+	if strings.Contains(out, "fs_batch_size_histogram_count{}") {
+		t.Fatalf("unexpected empty label set for batch count metric")
+	}
+	if strings.Contains(out, "fs_gc_duration_seconds_sum{}") {
+		t.Fatalf("unexpected empty label set for gc sum metric")
+	}
+	if strings.Contains(out, "fs_gc_duration_seconds_count{}") {
+		t.Fatalf("unexpected empty label set for gc count metric")
+	}
+}
+
+func TestEscapeLabelValueEscapesSingleBackslash(t *testing.T) {
+	got := escapeLabelValue(`a\b`)
+	want := `a\\b`
+	if got != want {
+		t.Fatalf("escapeLabelValue returned %q, want %q", got, want)
+	}
+}

models/models.go

@@ -68,6 +68,23 @@ type ListBucketResult struct {
 	CommonPrefixes []CommonPrefixes `xml:"CommonPrefixes,omitempty"`
 }
 
+type ListBucketResultV1 struct {
+	XMLName xml.Name `xml:"ListBucketResult"`
+	Xmlns   string   `xml:"xmlns,attr"`
+
+	Name         string `xml:"Name"`
+	Prefix       string `xml:"Prefix"`
+	Marker       string `xml:"Marker,omitempty"`
+	NextMarker   string `xml:"NextMarker,omitempty"`
+	Delimiter    string `xml:"Delimiter,omitempty"`
+	MaxKeys      int    `xml:"MaxKeys"`
+	IsTruncated  bool   `xml:"IsTruncated"`
+	EncodingType string `xml:"EncodingType,omitempty"`
+
+	Contents       []Contents       `xml:"Contents,omitempty"`
+	CommonPrefixes []CommonPrefixes `xml:"CommonPrefixes,omitempty"`
+}
+
 type ListBucketResultV2 struct {
 	XMLName xml.Name `xml:"ListBucketResult"`
 	Xmlns   string   `xml:"xmlns,attr"`
@@ -183,3 +200,26 @@ type DeleteError struct {
 	Code    string `xml:"Code"`
 	Message string `xml:"Message"`
 }
+
+type AuthIdentity struct {
+	AccessKeyID string `json:"access_key_id"`
+	SecretEnc   string `json:"secret_enc"`
+	SecretNonce string `json:"secret_nonce"`
+	EncAlg      string `json:"enc_alg"`
+	KeyVersion  string `json:"key_version"`
+	Status      string `json:"status"`
+	CreatedAt   int64  `json:"created_at"`
+	UpdatedAt   int64  `json:"updated_at"`
+}
+
+type AuthPolicy struct {
+	Principal  string                `json:"principal"`
+	Statements []AuthPolicyStatement `json:"statements"`
+}
+
+type AuthPolicyStatement struct {
+	Effect  string   `json:"effect"`
+	Actions []string `json:"actions"`
+	Bucket  string   `json:"bucket"`
+	Prefix  string   `json:"prefix"`
+}

service/service.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"fs/metadata"
+	"fs/metrics"
 	"fs/models"
 	"fs/storage"
 	"io"
@@ -41,9 +42,37 @@ func NewObjectService(metadataHandler *metadata.MetadataHandler, blobHandler *st
 	}
 }
 
-func (s *ObjectService) PutObject(bucket, key, contentType string, input io.Reader) (*models.ObjectManifest, error) {
+func (s *ObjectService) acquireGCRLock() func() {
+	waitStart := time.Now()
 	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
+	metrics.Default.ObserveLockWait("gc_mu_read", time.Since(waitStart))
+	holdStart := time.Now()
+	return func() {
+		metrics.Default.ObserveLockHold("gc_mu_read", time.Since(holdStart))
+		s.gcMu.RUnlock()
+	}
+}
+
+func (s *ObjectService) acquireGCLock() func() {
+	waitStart := time.Now()
+	s.gcMu.Lock()
+	metrics.Default.ObserveLockWait("gc_mu_write", time.Since(waitStart))
+	holdStart := time.Now()
+	return func() {
+		metrics.Default.ObserveLockHold("gc_mu_write", time.Since(holdStart))
+		s.gcMu.Unlock()
+	}
+}
+
+func (s *ObjectService) PutObject(bucket, key, contentType string, input io.Reader) (*models.ObjectManifest, error) {
+	start := time.Now()
+	success := false
+	defer func() {
+		metrics.Default.ObserveService("put_object", time.Since(start), success)
+	}()
+
+	unlock := s.acquireGCRLock()
+	defer unlock()
 
 	chunks, size, etag, err := s.blob.IngestStream(input)
 	if err != nil {
@@ -71,110 +100,171 @@ func (s *ObjectService) PutObject(bucket, key, contentType string, input io.Read
 		return nil, err
 	}
 
+	success = true
 	return manifest, nil
 }
 
 func (s *ObjectService) GetObject(bucket, key string) (io.ReadCloser, *models.ObjectManifest, error) {
+	start := time.Now()
+
+	waitStart := time.Now()
 	s.gcMu.RLock()
+	metrics.Default.ObserveLockWait("gc_mu_read", time.Since(waitStart))
+	holdStart := time.Now()
 
 	manifest, err := s.metadata.GetManifest(bucket, key)
 	if err != nil {
+		metrics.Default.ObserveLockHold("gc_mu_read", time.Since(holdStart))
 		s.gcMu.RUnlock()
+		metrics.Default.ObserveService("get_object", time.Since(start), false)
 		return nil, nil, err
 	}
 	pr, pw := io.Pipe()
 
 	go func() {
+		streamOK := false
+		defer func() {
+			metrics.Default.ObserveService("get_object", time.Since(start), streamOK)
+		}()
+		defer metrics.Default.ObserveLockHold("gc_mu_read", time.Since(holdStart))
 		defer s.gcMu.RUnlock()
 		if err := s.blob.AssembleStream(manifest.Chunks, pw); err != nil {
 			_ = pw.CloseWithError(err)
 			return
 		}
-		_ = pw.Close()
+		if err := pw.Close(); err != nil {
+			return
+		}
+		streamOK = true
 	}()
 	return pr, manifest, nil
 }
 
 func (s *ObjectService) HeadObject(bucket, key string) (models.ObjectManifest, error) {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
+	start := time.Now()
+	success := false
+	defer func() {
+		metrics.Default.ObserveService("head_object", time.Since(start), success)
+	}()
+
+	unlock := s.acquireGCRLock()
+	defer unlock()
 
 	manifest, err := s.metadata.GetManifest(bucket, key)
 	if err != nil {
 		return models.ObjectManifest{}, err
 	}
+	success = true
 	return *manifest, nil
 }
 
 func (s *ObjectService) DeleteObject(bucket, key string) error {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
-	return s.metadata.DeleteManifest(bucket, key)
+	start := time.Now()
+	success := false
+	defer func() {
+		metrics.Default.ObserveService("delete_object", time.Since(start), success)
+	}()
+
+	unlock := s.acquireGCRLock()
+	defer unlock()
+	err := s.metadata.DeleteManifest(bucket, key)
+	success = err == nil
+	return err
 }
 
 func (s *ObjectService) ListObjects(bucket, prefix string) ([]*models.ObjectManifest, error) {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
+	unlock := s.acquireGCRLock()
+	defer unlock()
 
 	return s.metadata.ListObjects(bucket, prefix)
 }
 
 func (s *ObjectService) ForEachObjectFrom(bucket, startKey string, fn func(*models.ObjectManifest) error) error {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
+	start := time.Now()
+	success := false
+	defer func() {
+		metrics.Default.ObserveService("for_each_object_from", time.Since(start), success)
+	}()
 
-	return s.metadata.ForEachObjectFrom(bucket, startKey, fn)
+	unlock := s.acquireGCRLock()
+	defer unlock()
+
+	err := s.metadata.ForEachObjectFrom(bucket, startKey, fn)
+	success = err == nil
+	return err
 }
 
 func (s *ObjectService) CreateBucket(bucket string) error {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
-	return s.metadata.CreateBucket(bucket)
+	start := time.Now()
+	success := false
+	defer func() {
+		metrics.Default.ObserveService("create_bucket", time.Since(start), success)
+	}()
+
+	unlock := s.acquireGCRLock()
+	defer unlock()
+	err := s.metadata.CreateBucket(bucket)
+	success = err == nil
+	return err
 }
 
 func (s *ObjectService) HeadBucket(bucket string) error {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
+	unlock := s.acquireGCRLock()
+	defer unlock()
 
 	_, err := s.metadata.GetBucketManifest(bucket)
 	return err
 }
 
 func (s *ObjectService) GetBucketManifest(bucket string) (*models.BucketManifest, error) {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
+	unlock := s.acquireGCRLock()
+	defer unlock()
 
 	return s.metadata.GetBucketManifest(bucket)
 }
 
 func (s *ObjectService) DeleteBucket(bucket string) error {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
+	unlock := s.acquireGCRLock()
+	defer unlock()
 	return s.metadata.DeleteBucket(bucket)
 }
 
 func (s *ObjectService) ListBuckets() ([]string, error) {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
+	start := time.Now()
+	success := false
+	defer func() {
+		metrics.Default.ObserveService("list_buckets", time.Since(start), success)
+	}()
 
-	return s.metadata.ListBuckets()
+	unlock := s.acquireGCRLock()
+	defer unlock()
+
+	buckets, err := s.metadata.ListBuckets()
+	success = err == nil
+	return buckets, err
 }
 
 func (s *ObjectService) DeleteObjects(bucket string, keys []string) ([]string, error) {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
+	unlock := s.acquireGCRLock()
+	defer unlock()
 	return s.metadata.DeleteManifests(bucket, keys)
 }
 
 func (s *ObjectService) CreateMultipartUpload(bucket, key string) (*models.MultipartUpload, error) {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
+	unlock := s.acquireGCRLock()
+	defer unlock()
 	return s.metadata.CreateMultipartUpload(bucket, key)
 }
 
 func (s *ObjectService) UploadPart(bucket, key, uploadId string, partNumber int, input io.Reader) (string, error) {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
+	start := time.Now()
+	success := false
+	defer func() {
+		metrics.Default.ObserveService("upload_part", time.Since(start), success)
+	}()
+
+	unlock := s.acquireGCRLock()
+	defer unlock()
 
 	if partNumber < 1 || partNumber > 10000 {
 		return "", ErrInvalidPart
@@ -204,12 +294,13 @@ func (s *ObjectService) UploadPart(bucket, key, uploadId string, partNumber int,
 	if err != nil {
 		return "", err
 	}
+	success = true
 	return etag, nil
 }
 
 func (s *ObjectService) ListMultipartParts(bucket, key, uploadID string) ([]models.UploadedPart, error) {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
+	unlock := s.acquireGCRLock()
+	defer unlock()
 
 	upload, err := s.metadata.GetMultipartUpload(uploadID)
 	if err != nil {
@@ -222,8 +313,14 @@ func (s *ObjectService) ListMultipartParts(bucket, key, uploadID string) ([]mode
 }
 
 func (s *ObjectService) CompleteMultipartUpload(bucket, key, uploadID string, completed []models.CompletedPart) (*models.ObjectManifest, error) {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
+	start := time.Now()
+	success := false
+	defer func() {
+		metrics.Default.ObserveService("complete_multipart_upload", time.Since(start), success)
+	}()
+
+	unlock := s.acquireGCRLock()
+	defer unlock()
 
 	if len(completed) == 0 {
 		return nil, ErrInvalidCompleteRequest
@@ -288,12 +385,13 @@ func (s *ObjectService) CompleteMultipartUpload(bucket, key, uploadID string, co
 		return nil, err
 	}
 
+	success = true
 	return manifest, nil
 }
 
 func (s *ObjectService) AbortMultipartUpload(bucket, key, uploadID string) error {
-	s.gcMu.RLock()
-	defer s.gcMu.RUnlock()
+	unlock := s.acquireGCRLock()
+	defer unlock()
 
 	upload, err := s.metadata.GetMultipartUpload(uploadID)
 	if err != nil {
@@ -327,8 +425,17 @@ func (s *ObjectService) Close() error {
 }
 
 func (s *ObjectService) GarbageCollect() error {
-	s.gcMu.Lock()
-	defer s.gcMu.Unlock()
+	start := time.Now()
+	success := false
+	deletedChunks := 0
+	deleteErrors := 0
+	cleanedUploads := 0
+	defer func() {
+		metrics.Default.ObserveGC(time.Since(start), deletedChunks, deleteErrors, cleanedUploads, success)
+	}()
+
+	unlock := s.acquireGCLock()
+	defer unlock()
 
 	referencedChunkSet, err := s.metadata.GetReferencedChunkSet()
 	if err != nil {
@@ -336,9 +443,6 @@ func (s *ObjectService) GarbageCollect() error {
 	}
 
 	totalChunks := 0
-	deletedChunks := 0
-	deleteErrors := 0
-	cleanedUploads := 0
 
 	if err := s.blob.ForEachChunk(func(chunkID string) error {
 		totalChunks++
@@ -368,6 +472,7 @@ func (s *ObjectService) GarbageCollect() error {
 		"delete_errors", deleteErrors,
 		"cleaned_uploads", cleanedUploads,
 	)
+	success = true
 	return nil
 }
 

storage/blob.go

@@ -6,10 +6,12 @@ import (
 	"encoding/hex"
 	"errors"
 	"fmt"
+	"fs/metrics"
 	"io"
 	"os"
 	"path/filepath"
 	"strings"
+	"time"
 )
 
 const blobRoot = "blobs"
@@ -37,11 +39,16 @@ func NewBlobStore(root string, chunkSize int) (*BlobStore, error) {
 }
 
 func (bs *BlobStore) IngestStream(stream io.Reader) ([]string, int64, string, error) {
+	start := time.Now()
 	fullFileHasher := md5.New()
 
 	buffer := make([]byte, bs.chunkSize)
 	var totalSize int64
 	var chunkIDs []string
+	success := false
+	defer func() {
+		metrics.Default.ObserveBlob("ingest_stream", time.Since(start), 0, success)
+	}()
 
 	for {
 		bytesRead, err := io.ReadFull(stream, buffer)
@@ -74,10 +81,18 @@ func (bs *BlobStore) IngestStream(stream io.Reader) ([]string, int64, string, er
 	}
 
 	etag := hex.EncodeToString(fullFileHasher.Sum(nil))
+	success = true
 	return chunkIDs, totalSize, etag, nil
 }
 
 func (bs *BlobStore) saveBlob(chunkID string, data []byte) error {
+	start := time.Now()
+	success := false
+	writtenBytes := int64(0)
+	defer func() {
+		metrics.Default.ObserveBlob("write_chunk", time.Since(start), writtenBytes, success)
+	}()
+
 	if !isValidChunkID(chunkID) {
 		return fmt.Errorf("invalid chunk id: %q", chunkID)
 	}
@@ -88,6 +103,7 @@ func (bs *BlobStore) saveBlob(chunkID string, data []byte) error {
 
 	fullPath := filepath.Join(dir, chunkID)
 	if _, err := os.Stat(fullPath); err == nil {
+		success = true
 		return nil
 	} else if !os.IsNotExist(err) {
 		return err
@@ -119,6 +135,7 @@ func (bs *BlobStore) saveBlob(chunkID string, data []byte) error {
 
 	if err := os.Rename(tmpPath, fullPath); err != nil {
 		if _, statErr := os.Stat(fullPath); statErr == nil {
+			success = true
 			return nil
 		}
 		return err
@@ -128,10 +145,18 @@ func (bs *BlobStore) saveBlob(chunkID string, data []byte) error {
 	if err := syncDir(dir); err != nil {
 		return err
 	}
+	writtenBytes = int64(len(data))
+	success = true
 	return nil
 }
 
 func (bs *BlobStore) AssembleStream(chunkIDs []string, w *io.PipeWriter) error {
+	start := time.Now()
+	success := false
+	defer func() {
+		metrics.Default.ObserveBlob("assemble_stream", time.Since(start), 0, success)
+	}()
+
 	for _, chunkID := range chunkIDs {
 		chunkData, err := bs.GetBlob(chunkID)
 		if err != nil {
@@ -141,14 +166,28 @@ func (bs *BlobStore) AssembleStream(chunkIDs []string, w *io.PipeWriter) error {
 			return err
 		}
 	}
+	success = true
 	return nil
 }
 
 func (bs *BlobStore) GetBlob(chunkID string) ([]byte, error) {
+	start := time.Now()
+	success := false
+	var size int64
+	defer func() {
+		metrics.Default.ObserveBlob("read_chunk", time.Since(start), size, success)
+	}()
+
 	if !isValidChunkID(chunkID) {
 		return nil, fmt.Errorf("invalid chunk id: %q", chunkID)
 	}
-	return os.ReadFile(filepath.Join(bs.dataRoot, blobRoot, chunkID[:2], chunkID[2:4], chunkID))
+	data, err := os.ReadFile(filepath.Join(bs.dataRoot, blobRoot, chunkID[:2], chunkID[2:4], chunkID))
+	if err != nil {
+		return nil, err
+	}
+	size = int64(len(data))
+	success = true
+	return data, nil
 }
 
 func (bs *BlobStore) DeleteBlob(chunkID string) error {

utils/config.go

@@ -21,6 +21,15 @@ type Config struct {
 	GcInterval                time.Duration
 	GcEnabled                 bool
 	MultipartCleanupRetention time.Duration
+	AuthEnabled               bool
+	AuthRegion                string
+	AuthSkew                  time.Duration
+	AuthMaxPresign            time.Duration
+	AuthMasterKey             string
+	AuthBootstrapAccessKey    string
+	AuthBootstrapSecretKey    string
+	AuthBootstrapPolicy       string
+	AdminAPIEnabled           bool
 }
 
 func NewConfig() *Config {
@@ -39,6 +48,15 @@ func NewConfig() *Config {
 		MultipartCleanupRetention: time.Duration(
 			envIntRange("MULTIPART_RETENTION_HOURS", 24, 1, 24*30),
 		) * time.Hour,
+		AuthEnabled:            envBool("AUTH_ENABLED", false),
+		AuthRegion:             firstNonEmpty(strings.TrimSpace(os.Getenv("AUTH_REGION")), "us-east-1"),
+		AuthSkew:               time.Duration(envIntRange("AUTH_SKEW_SECONDS", 300, 30, 3600)) * time.Second,
+		AuthMaxPresign:         time.Duration(envIntRange("AUTH_MAX_PRESIGN_SECONDS", 86400, 60, 86400)) * time.Second,
+		AuthMasterKey:          strings.TrimSpace(os.Getenv("AUTH_MASTER_KEY")),
+		AuthBootstrapAccessKey: strings.TrimSpace(os.Getenv("AUTH_BOOTSTRAP_ACCESS_KEY")),
+		AuthBootstrapSecretKey: strings.TrimSpace(os.Getenv("AUTH_BOOTSTRAP_SECRET_KEY")),
+		AuthBootstrapPolicy:    strings.TrimSpace(os.Getenv("AUTH_BOOTSTRAP_POLICY")),
+		AdminAPIEnabled:        envBool("ADMIN_API_ENABLED", true),
 	}
 
 	if config.LogFormat != "json" && config.LogFormat != "text" {