feat(webhook): HMAC-SHA256 signature verification on inbound webhooks

Adds an opt-in inbound HMAC scheme so a leaked URL alone is not enough
to forge deploy/sync requests — the caller must also know a separate
signing secret. Header format is X-Hub-Signature-256, matching the
Gitea/GitHub/GitLab convention so existing CI integrations work without
custom code.

Behaviour:
- per-project / per-site signing_secret is independent of the URL secret
- require_signature flag does a hard 401 on missing/invalid signatures
- even when require_signature is off, an *invalid* submitted signature
  returns 401 — surfaces CI misconfiguration instead of silently passing
- comparison uses subtle/hmac.Equal (constant time)

Backend:
- store: webhook_signing_secret + webhook_require_signature columns on
  projects + static_sites; scanProject helper, scan helpers updated; new
  Set* helpers for both fields
- webhook/handler: verifyHMAC helper, body read once, integrated into
  both project and site handlers
- api: per-entity signing-secret rotate / disable / require-toggle
  endpoints under /api/{projects,sites}/{id}/webhook/...

Frontend:
- WebhookPanel gains optional signing handlers (no breaking change for
  existing callers; signing UI hides when handlers aren't wired)
- one-shot reveal of the issued secret with copy + dismiss
- ToggleSwitch for require-signature, disabled until a secret is issued
- en/ru i18n strings

Tests:
- HMACRequiredAndValid (200 + deploy fires)
- HMACRequiredButMissing (401, no deploy)
- HMACPresentButWrong (401 even when require_signature=false)
- HMACOptionalUnsignedAccepted (200 when neither configured)

internal/api/router.go

@@ -245,6 +245,10 @@ func (s *Server) Router() chi.Router {
 					// Per-project webhook URL management.
 					r.Get("/webhook", s.getProjectWebhook)
 					r.Post("/webhook/regenerate", s.regenerateProjectWebhook)
+					// Inbound HMAC signing — secret rotation + enforcement toggle.
+					r.Post("/webhook/signing-secret/regenerate", s.regenerateProjectSigningSecret)
+					r.Delete("/webhook/signing-secret", s.disableProjectSigningSecret)
+					r.Put("/webhook/require-signature", s.updateProjectSigningRequirement)
 
 					// Per-project outgoing-webhook signing & test.
 					r.Get("/notification-secret", s.getProjectNotificationSecret)
@@ -325,6 +329,9 @@ func (s *Server) Router() chi.Router {
 					r.Post("/start", s.startStaticSite)
 					r.Get("/webhook", s.getStaticSiteWebhook)
 					r.Post("/webhook/regenerate", s.regenerateStaticSiteWebhook)
+					r.Post("/webhook/signing-secret/regenerate", s.regenerateStaticSiteSigningSecret)
+					r.Delete("/webhook/signing-secret", s.disableStaticSiteSigningSecret)
+					r.Put("/webhook/require-signature", s.updateStaticSiteSigningRequirement)
 
 					// Per-site outgoing-webhook signing & test.
 					r.Get("/notification-secret", s.getStaticSiteNotificationSecret)

internal/api/webhooks.go

@@ -27,8 +27,20 @@ func generateWebhookSecret() string {
 // Clients never see raw secrets except at issue/rotate time via these fields;
 // the URL shape is "/api/webhook/..." so callers can prepend their own origin.
 type webhookURLResponse struct {
-	WebhookURL    string `json:"webhook_url"`
-	WebhookSecret string `json:"webhook_secret"`
+	WebhookURL              string `json:"webhook_url"`
+	WebhookSecret           string `json:"webhook_secret"`
+	HasSigningSecret        bool   `json:"has_signing_secret"`
+	WebhookRequireSignature bool   `json:"webhook_require_signature"`
+}
+
+// signingSecretResponse is returned when a signing secret is issued or rotated.
+type signingSecretResponse struct {
+	SigningSecret string `json:"signing_secret"`
+}
+
+// signingToggleRequest is the body of the require-signature toggle endpoint.
+type signingToggleRequest struct {
+	RequireSignature bool `json:"require_signature"`
 }
 
 // getProjectWebhook handles GET /api/projects/{id}/webhook.
@@ -48,12 +60,97 @@ func (s *Server) getProjectWebhook(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	project, err := s.store.GetProjectByID(id)
+	if err != nil {
+		respondError(w, http.StatusInternalServerError, "failed to get project")
+		return
+	}
+
 	respondJSON(w, http.StatusOK, webhookURLResponse{
-		WebhookURL:    "/api/webhook/" + secret,
-		WebhookSecret: secret,
+		WebhookURL:              "/api/webhook/" + secret,
+		WebhookSecret:           secret,
+		HasSigningSecret:        project.WebhookSigningSecret != "",
+		WebhookRequireSignature: project.WebhookRequireSignature,
 	})
 }
 
+// regenerateProjectSigningSecret handles POST /api/projects/{id}/webhook/signing-secret/regenerate.
+// Issues a fresh HMAC signing secret for inbound webhook verification. The
+// secret is returned exactly once — the UI is responsible for letting the
+// user copy it into their CI configuration.
+func (s *Server) regenerateProjectSigningSecret(w http.ResponseWriter, r *http.Request) {
+	id := chi.URLParam(r, "id")
+	if _, err := s.store.GetProjectByID(id); err != nil {
+		if errors.Is(err, store.ErrNotFound) {
+			respondNotFound(w, "project")
+			return
+		}
+		respondError(w, http.StatusInternalServerError, "failed to get project")
+		return
+	}
+	secret := generateWebhookSecret()
+	if err := s.store.SetProjectWebhookSigningSecret(id, secret); err != nil {
+		slog.Error("rotate project signing secret", "project", id, "error", err)
+		respondError(w, http.StatusInternalServerError, "failed to rotate signing secret")
+		return
+	}
+	slog.Info("project webhook signing secret rotated", "project", id)
+	respondJSON(w, http.StatusOK, signingSecretResponse{SigningSecret: secret})
+}
+
+// disableProjectSigningSecret handles DELETE /api/projects/{id}/webhook/signing-secret.
+// Clears the HMAC signing secret and disables enforcement.
+func (s *Server) disableProjectSigningSecret(w http.ResponseWriter, r *http.Request) {
+	id := chi.URLParam(r, "id")
+	if err := s.store.SetProjectWebhookSigningSecret(id, ""); err != nil {
+		if errors.Is(err, store.ErrNotFound) {
+			respondNotFound(w, "project")
+			return
+		}
+		respondError(w, http.StatusInternalServerError, "failed to clear signing secret")
+		return
+	}
+	if err := s.store.SetProjectWebhookRequireSignature(id, false); err != nil {
+		slog.Warn("disable project require_signature", "project", id, "error", err)
+	}
+	respondJSON(w, http.StatusOK, map[string]bool{"success": true})
+}
+
+// updateProjectSigningRequirement handles PUT /api/projects/{id}/webhook/require-signature.
+// Toggles whether unsigned/invalidly-signed inbound webhook requests are
+// rejected with 401.
+func (s *Server) updateProjectSigningRequirement(w http.ResponseWriter, r *http.Request) {
+	id := chi.URLParam(r, "id")
+	var req signingToggleRequest
+	if !decodeJSON(w, r, &req) {
+		return
+	}
+	if req.RequireSignature {
+		project, err := s.store.GetProjectByID(id)
+		if err != nil {
+			if errors.Is(err, store.ErrNotFound) {
+				respondNotFound(w, "project")
+				return
+			}
+			respondError(w, http.StatusInternalServerError, "failed to get project")
+			return
+		}
+		if project.WebhookSigningSecret == "" {
+			respondError(w, http.StatusBadRequest, "issue a signing secret before enabling enforcement")
+			return
+		}
+	}
+	if err := s.store.SetProjectWebhookRequireSignature(id, req.RequireSignature); err != nil {
+		if errors.Is(err, store.ErrNotFound) {
+			respondNotFound(w, "project")
+			return
+		}
+		respondError(w, http.StatusInternalServerError, "failed to update setting")
+		return
+	}
+	respondJSON(w, http.StatusOK, map[string]bool{"success": true})
+}
+
 // regenerateProjectWebhook handles POST /api/projects/{id}/webhook/regenerate.
 // Rotates the project's webhook secret, invalidating the old URL.
 func (s *Server) regenerateProjectWebhook(w http.ResponseWriter, r *http.Request) {
@@ -99,12 +196,91 @@ func (s *Server) getStaticSiteWebhook(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	site, err := s.store.GetStaticSiteByID(id)
+	if err != nil {
+		respondError(w, http.StatusInternalServerError, "failed to get static site")
+		return
+	}
+
 	respondJSON(w, http.StatusOK, webhookURLResponse{
-		WebhookURL:    "/api/webhook/sites/" + secret,
-		WebhookSecret: secret,
+		WebhookURL:              "/api/webhook/sites/" + secret,
+		WebhookSecret:           secret,
+		HasSigningSecret:        site.WebhookSigningSecret != "",
+		WebhookRequireSignature: site.WebhookRequireSignature,
 	})
 }
 
+// regenerateStaticSiteSigningSecret handles POST /api/sites/{id}/webhook/signing-secret/regenerate.
+func (s *Server) regenerateStaticSiteSigningSecret(w http.ResponseWriter, r *http.Request) {
+	id := chi.URLParam(r, "id")
+	if _, err := s.store.GetStaticSiteByID(id); err != nil {
+		if errors.Is(err, store.ErrNotFound) {
+			respondNotFound(w, "static site")
+			return
+		}
+		respondError(w, http.StatusInternalServerError, "failed to get static site")
+		return
+	}
+	secret := generateWebhookSecret()
+	if err := s.store.SetStaticSiteWebhookSigningSecret(id, secret); err != nil {
+		slog.Error("rotate site signing secret", "site", id, "error", err)
+		respondError(w, http.StatusInternalServerError, "failed to rotate signing secret")
+		return
+	}
+	slog.Info("static site webhook signing secret rotated", "site", id)
+	respondJSON(w, http.StatusOK, signingSecretResponse{SigningSecret: secret})
+}
+
+// disableStaticSiteSigningSecret handles DELETE /api/sites/{id}/webhook/signing-secret.
+func (s *Server) disableStaticSiteSigningSecret(w http.ResponseWriter, r *http.Request) {
+	id := chi.URLParam(r, "id")
+	if err := s.store.SetStaticSiteWebhookSigningSecret(id, ""); err != nil {
+		if errors.Is(err, store.ErrNotFound) {
+			respondNotFound(w, "static site")
+			return
+		}
+		respondError(w, http.StatusInternalServerError, "failed to clear signing secret")
+		return
+	}
+	if err := s.store.SetStaticSiteWebhookRequireSignature(id, false); err != nil {
+		slog.Warn("disable site require_signature", "site", id, "error", err)
+	}
+	respondJSON(w, http.StatusOK, map[string]bool{"success": true})
+}
+
+// updateStaticSiteSigningRequirement handles PUT /api/sites/{id}/webhook/require-signature.
+func (s *Server) updateStaticSiteSigningRequirement(w http.ResponseWriter, r *http.Request) {
+	id := chi.URLParam(r, "id")
+	var req signingToggleRequest
+	if !decodeJSON(w, r, &req) {
+		return
+	}
+	if req.RequireSignature {
+		site, err := s.store.GetStaticSiteByID(id)
+		if err != nil {
+			if errors.Is(err, store.ErrNotFound) {
+				respondNotFound(w, "static site")
+				return
+			}
+			respondError(w, http.StatusInternalServerError, "failed to get static site")
+			return
+		}
+		if site.WebhookSigningSecret == "" {
+			respondError(w, http.StatusBadRequest, "issue a signing secret before enabling enforcement")
+			return
+		}
+	}
+	if err := s.store.SetStaticSiteWebhookRequireSignature(id, req.RequireSignature); err != nil {
+		if errors.Is(err, store.ErrNotFound) {
+			respondNotFound(w, "static site")
+			return
+		}
+		respondError(w, http.StatusInternalServerError, "failed to update setting")
+		return
+	}
+	respondJSON(w, http.StatusOK, map[string]bool{"success": true})
+}
+
 // regenerateStaticSiteWebhook handles POST /api/sites/{id}/webhook/regenerate.
 func (s *Server) regenerateStaticSiteWebhook(w http.ResponseWriter, r *http.Request) {
 	id := chi.URLParam(r, "id")

internal/store/models.go

@@ -11,7 +11,9 @@ type Project struct {
 	Env              string `json:"env"`     // JSON-encoded map
 	Volumes          string `json:"volumes"` // JSON-encoded map
 	NpmAccessListID     int    `json:"npm_access_list_id"` // per-project override, 0 = use global
-	WebhookSecret       string `json:"-"`                  // per-project webhook secret; never serialized directly
+	WebhookSecret       string `json:"-"`                  // per-project webhook secret (URL identifier); never serialized
+	WebhookSigningSecret    string `json:"-"`                       // HMAC-SHA256 key for inbound webhook signature verification; never serialized
+	WebhookRequireSignature bool   `json:"webhook_require_signature"` // if true, reject unsigned/invalid-sig webhook requests
 	NotificationURL     string `json:"notification_url"`    // outgoing webhook target; empty = inherit from settings
 	NotificationSecret  string `json:"-"`                  // outgoing-webhook signing secret; never serialized directly
 	CreatedAt        string `json:"created_at"`
@@ -258,7 +260,9 @@ type StaticSite struct {
 	Error          string `json:"error"`
 	StorageEnabled bool   `json:"storage_enabled"`
 	StorageLimitMB int    `json:"storage_limit_mb"` // 0 = unlimited
-	WebhookSecret      string `json:"-"`                 // per-site webhook secret; never serialized directly
+	WebhookSecret      string `json:"-"`                 // per-site webhook secret (URL identifier); never serialized
+	WebhookSigningSecret    string `json:"-"`                       // HMAC-SHA256 key for inbound webhook signature verification; never serialized
+	WebhookRequireSignature bool   `json:"webhook_require_signature"` // if true, reject unsigned/invalid-sig webhook requests
 	NotificationURL    string `json:"notification_url"`   // outgoing webhook target; empty = inherit from settings
 	NotificationSecret string `json:"-"`                 // outgoing-webhook signing secret; never serialized directly
 	CreatedAt      string `json:"created_at"`

internal/store/projects.go

@@ -31,7 +31,27 @@ func generateWebhookSecret() string {
 
 // projectCols is the canonical column list for projects queries.
 const projectCols = `id, name, registry, image, port, healthcheck, env, volumes,
-	npm_access_list_id, webhook_secret, notification_url, notification_secret, created_at, updated_at`
+	npm_access_list_id, webhook_secret, webhook_signing_secret, webhook_require_signature,
+	notification_url, notification_secret, created_at, updated_at`
+
+// rowScanner is the subset of *sql.Row / *sql.Rows used by scanProject.
+type rowScanner interface {
+	Scan(dest ...any) error
+}
+
+// scanProject reads one row in projectCols order. webhook_require_signature
+// is stored as INTEGER and converted to bool here.
+func scanProject(r rowScanner) (Project, error) {
+	var p Project
+	var requireSig int
+	if err := r.Scan(&p.ID, &p.Name, &p.Registry, &p.Image, &p.Port, &p.Healthcheck, &p.Env, &p.Volumes,
+		&p.NpmAccessListID, &p.WebhookSecret, &p.WebhookSigningSecret, &requireSig,
+		&p.NotificationURL, &p.NotificationSecret, &p.CreatedAt, &p.UpdatedAt); err != nil {
+		return Project{}, err
+	}
+	p.WebhookRequireSignature = requireSig != 0
+	return p, nil
+}
 
 // CreateProject inserts a new project and returns it. A webhook secret is
 // generated automatically if one is not already set on the input.
@@ -45,11 +65,16 @@ func (s *Store) CreateProject(p Project) (Project, error) {
 		return Project{}, fmt.Errorf("webhook_secret must be at least %d characters", minWebhookSecretLength)
 	}
 
+	requireSig := 0
+	if p.WebhookRequireSignature {
+		requireSig = 1
+	}
 	_, err := s.db.Exec(
 		`INSERT INTO projects (`+projectCols+`)
-		 VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+		 VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
 		p.ID, p.Name, p.Registry, p.Image, p.Port, p.Healthcheck, p.Env, p.Volumes,
-		p.NpmAccessListID, p.WebhookSecret, p.NotificationURL, p.NotificationSecret, p.CreatedAt, p.UpdatedAt,
+		p.NpmAccessListID, p.WebhookSecret, p.WebhookSigningSecret, requireSig,
+		p.NotificationURL, p.NotificationSecret, p.CreatedAt, p.UpdatedAt,
 	)
 	if err != nil {
 		return Project{}, fmt.Errorf("insert project: %w", err)
@@ -59,11 +84,8 @@ func (s *Store) CreateProject(p Project) (Project, error) {
 
 // GetProjectByID returns a single project by its ID.
 func (s *Store) GetProjectByID(id string) (Project, error) {
-	var p Project
-	err := s.db.QueryRow(
-		`SELECT `+projectCols+` FROM projects WHERE id = ?`, id,
-	).Scan(&p.ID, &p.Name, &p.Registry, &p.Image, &p.Port, &p.Healthcheck, &p.Env, &p.Volumes,
-		&p.NpmAccessListID, &p.WebhookSecret, &p.NotificationURL, &p.NotificationSecret, &p.CreatedAt, &p.UpdatedAt)
+	row := s.db.QueryRow(`SELECT `+projectCols+` FROM projects WHERE id = ?`, id)
+	p, err := scanProject(row)
 	if errors.Is(err, sql.ErrNoRows) {
 		return Project{}, fmt.Errorf("project %s: %w", id, ErrNotFound)
 	}
@@ -79,11 +101,8 @@ func (s *Store) GetProjectByWebhookSecret(secret string) (Project, error) {
 	if secret == "" {
 		return Project{}, ErrNotFound
 	}
-	var p Project
-	err := s.db.QueryRow(
-		`SELECT `+projectCols+` FROM projects WHERE webhook_secret = ?`, secret,
-	).Scan(&p.ID, &p.Name, &p.Registry, &p.Image, &p.Port, &p.Healthcheck, &p.Env, &p.Volumes,
-		&p.NpmAccessListID, &p.WebhookSecret, &p.NotificationURL, &p.NotificationSecret, &p.CreatedAt, &p.UpdatedAt)
+	row := s.db.QueryRow(`SELECT `+projectCols+` FROM projects WHERE webhook_secret = ?`, secret)
+	p, err := scanProject(row)
 	if errors.Is(err, sql.ErrNoRows) {
 		return Project{}, ErrNotFound
 	}
@@ -105,9 +124,8 @@ func (s *Store) GetAllProjects() ([]Project, error) {
 
 	projects := []Project{}
 	for rows.Next() {
-		var p Project
-		if err := rows.Scan(&p.ID, &p.Name, &p.Registry, &p.Image, &p.Port, &p.Healthcheck, &p.Env, &p.Volumes,
-			&p.NpmAccessListID, &p.WebhookSecret, &p.NotificationURL, &p.NotificationSecret, &p.CreatedAt, &p.UpdatedAt); err != nil {
+		p, err := scanProject(rows)
+		if err != nil {
 			return nil, fmt.Errorf("scan project: %w", err)
 		}
 		projects = append(projects, p)
@@ -127,9 +145,8 @@ func (s *Store) GetProjectsByImage(image string) ([]Project, error) {
 
 	projects := []Project{}
 	for rows.Next() {
-		var p Project
-		if err := rows.Scan(&p.ID, &p.Name, &p.Registry, &p.Image, &p.Port, &p.Healthcheck, &p.Env, &p.Volumes,
-			&p.NpmAccessListID, &p.WebhookSecret, &p.NotificationURL, &p.NotificationSecret, &p.CreatedAt, &p.UpdatedAt); err != nil {
+		p, err := scanProject(rows)
+		if err != nil {
 			return nil, fmt.Errorf("scan project: %w", err)
 		}
 		projects = append(projects, p)
@@ -176,6 +193,45 @@ func (s *Store) SetProjectWebhookSecret(id, secret string) error {
 	return nil
 }
 
+// SetProjectWebhookSigningSecret assigns the HMAC signing secret used to
+// verify inbound webhook payloads. Pass an empty string to clear it (which
+// also implicitly disables signature enforcement on the next request).
+func (s *Store) SetProjectWebhookSigningSecret(id, secret string) error {
+	result, err := s.db.Exec(
+		`UPDATE projects SET webhook_signing_secret=?, updated_at=? WHERE id=?`,
+		secret, Now(), id,
+	)
+	if err != nil {
+		return fmt.Errorf("set project webhook signing secret: %w", err)
+	}
+	n, _ := result.RowsAffected()
+	if n == 0 {
+		return fmt.Errorf("project %s: %w", id, ErrNotFound)
+	}
+	return nil
+}
+
+// SetProjectWebhookRequireSignature toggles whether unsigned (or
+// invalidly-signed) webhook requests are rejected with 401.
+func (s *Store) SetProjectWebhookRequireSignature(id string, require bool) error {
+	v := 0
+	if require {
+		v = 1
+	}
+	result, err := s.db.Exec(
+		`UPDATE projects SET webhook_require_signature=?, updated_at=? WHERE id=?`,
+		v, Now(), id,
+	)
+	if err != nil {
+		return fmt.Errorf("set project webhook require_signature: %w", err)
+	}
+	n, _ := result.RowsAffected()
+	if n == 0 {
+		return fmt.Errorf("project %s: %w", id, ErrNotFound)
+	}
+	return nil
+}
+
 // EnsureProjectWebhookSecret returns the current webhook secret for a project,
 // generating one on the fly if the stored value is empty (lazy backfill for
 // projects created before the per-project webhook migration).

internal/store/static_sites.go

@@ -13,7 +13,8 @@ import (
 const staticSiteCols = `id, name, provider, gitea_url, repo_owner, repo_name, branch, folder_path,
 	access_token, domain, mode, render_markdown, sync_trigger, tag_pattern,
 	container_id, proxy_route_id, status, last_sync_at, last_commit_sha, error,
-	storage_enabled, storage_limit_mb, webhook_secret,
+	storage_enabled, storage_limit_mb,
+	webhook_secret, webhook_signing_secret, webhook_require_signature,
 	notification_url, notification_secret,
 	created_at, updated_at`
 
@@ -31,13 +32,13 @@ func (s *Store) CreateStaticSite(site StaticSite) (StaticSite, error) {
 
 	_, err := s.db.Exec(
 		`INSERT INTO static_sites (`+staticSiteCols+`)
-		 VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+		 VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
 		site.ID, site.Name, site.Provider, site.GiteaURL, site.RepoOwner, site.RepoName,
 		site.Branch, site.FolderPath, site.AccessToken, site.Domain, site.Mode,
 		BoolToInt(site.RenderMarkdown), site.SyncTrigger, site.TagPattern,
 		site.ContainerID, site.ProxyRouteID, site.Status, site.LastSyncAt,
 		site.LastCommitSHA, site.Error, BoolToInt(site.StorageEnabled), site.StorageLimitMB,
-		site.WebhookSecret,
+		site.WebhookSecret, site.WebhookSigningSecret, BoolToInt(site.WebhookRequireSignature),
 		site.NotificationURL, site.NotificationSecret,
 		site.CreatedAt, site.UpdatedAt,
 	)
@@ -228,14 +229,14 @@ func (s *Store) DeleteStaticSite(id string) error {
 // scanStaticSiteRow scans a static site from a *sql.Row.
 func scanStaticSiteRow(row *sql.Row) (StaticSite, error) {
 	var site StaticSite
-	var renderMarkdown, storageEnabled int
+	var renderMarkdown, storageEnabled, requireSig int
 	err := row.Scan(
 		&site.ID, &site.Name, &site.Provider, &site.GiteaURL, &site.RepoOwner, &site.RepoName,
 		&site.Branch, &site.FolderPath, &site.AccessToken, &site.Domain, &site.Mode,
 		&renderMarkdown, &site.SyncTrigger, &site.TagPattern,
 		&site.ContainerID, &site.ProxyRouteID, &site.Status, &site.LastSyncAt,
 		&site.LastCommitSHA, &site.Error, &storageEnabled, &site.StorageLimitMB,
-		&site.WebhookSecret,
+		&site.WebhookSecret, &site.WebhookSigningSecret, &requireSig,
 		&site.NotificationURL, &site.NotificationSecret,
 		&site.CreatedAt, &site.UpdatedAt,
 	)
@@ -244,20 +245,21 @@ func scanStaticSiteRow(row *sql.Row) (StaticSite, error) {
 	}
 	site.RenderMarkdown = renderMarkdown != 0
 	site.StorageEnabled = storageEnabled != 0
+	site.WebhookRequireSignature = requireSig != 0
 	return site, nil
 }
 
 // scanStaticSiteRows scans a static site from a *sql.Rows cursor.
 func scanStaticSiteRows(rows *sql.Rows) (StaticSite, error) {
 	var site StaticSite
-	var renderMarkdown, storageEnabled int
+	var renderMarkdown, storageEnabled, requireSig int
 	err := rows.Scan(
 		&site.ID, &site.Name, &site.Provider, &site.GiteaURL, &site.RepoOwner, &site.RepoName,
 		&site.Branch, &site.FolderPath, &site.AccessToken, &site.Domain, &site.Mode,
 		&renderMarkdown, &site.SyncTrigger, &site.TagPattern,
 		&site.ContainerID, &site.ProxyRouteID, &site.Status, &site.LastSyncAt,
 		&site.LastCommitSHA, &site.Error, &storageEnabled, &site.StorageLimitMB,
-		&site.WebhookSecret,
+		&site.WebhookSecret, &site.WebhookSigningSecret, &requireSig,
 		&site.NotificationURL, &site.NotificationSecret,
 		&site.CreatedAt, &site.UpdatedAt,
 	)
@@ -266,9 +268,48 @@ func scanStaticSiteRows(rows *sql.Rows) (StaticSite, error) {
 	}
 	site.RenderMarkdown = renderMarkdown != 0
 	site.StorageEnabled = storageEnabled != 0
+	site.WebhookRequireSignature = requireSig != 0
 	return site, nil
 }
 
+// SetStaticSiteWebhookSigningSecret assigns the inbound HMAC signing secret.
+// Pass an empty string to clear it (also implicitly disables enforcement).
+func (s *Store) SetStaticSiteWebhookSigningSecret(id, secret string) error {
+	result, err := s.db.Exec(
+		`UPDATE static_sites SET webhook_signing_secret=?, updated_at=? WHERE id=?`,
+		secret, Now(), id,
+	)
+	if err != nil {
+		return fmt.Errorf("set static site webhook signing secret: %w", err)
+	}
+	n, _ := result.RowsAffected()
+	if n == 0 {
+		return fmt.Errorf("static site %s: %w", id, ErrNotFound)
+	}
+	return nil
+}
+
+// SetStaticSiteWebhookRequireSignature toggles whether unsigned (or
+// invalidly-signed) inbound webhook requests are rejected with 401.
+func (s *Store) SetStaticSiteWebhookRequireSignature(id string, require bool) error {
+	v := 0
+	if require {
+		v = 1
+	}
+	result, err := s.db.Exec(
+		`UPDATE static_sites SET webhook_require_signature=?, updated_at=? WHERE id=?`,
+		v, Now(), id,
+	)
+	if err != nil {
+		return fmt.Errorf("set static site webhook require_signature: %w", err)
+	}
+	n, _ := result.RowsAffected()
+	if n == 0 {
+		return fmt.Errorf("static site %s: %w", id, ErrNotFound)
+	}
+	return nil
+}
+
 // SetStaticSiteNotificationSecret rotates the static site's outgoing-webhook
 // signing secret. Empty string disables HMAC signing for this site
 // (notifications still send unsigned, falling through to global resolution).

internal/store/store.go

@@ -151,6 +151,14 @@ func (s *Store) runMigrations() error {
 		// triggers a "pre-deploy" Tinyforge DB backup before any project deploy
 		// so a corrupted deploy is recoverable without data loss.
 		`ALTER TABLE settings ADD COLUMN auto_backup_before_deploy INTEGER NOT NULL DEFAULT 0`,
+		// Per-entity inbound HMAC signing (2026-05-07). webhook_signing_secret
+		// is the HMAC-SHA256 key separate from the URL secret so a leaked URL
+		// alone is not sufficient to forge a valid request. require_signature
+		// rejects unsigned requests when set (defense-in-depth opt-in).
+		`ALTER TABLE projects ADD COLUMN webhook_signing_secret TEXT NOT NULL DEFAULT ''`,
+		`ALTER TABLE projects ADD COLUMN webhook_require_signature INTEGER NOT NULL DEFAULT 0`,
+		`ALTER TABLE static_sites ADD COLUMN webhook_signing_secret TEXT NOT NULL DEFAULT ''`,
+		`ALTER TABLE static_sites ADD COLUMN webhook_require_signature INTEGER NOT NULL DEFAULT 0`,
 	}
 
 	// Additive stack tables (2026-04-16). Created here rather than in the

internal/webhook/handler.go

@@ -2,6 +2,9 @@ package webhook
 
 import (
 	"context"
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/hex"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -16,6 +19,47 @@ import (
 	"github.com/alexei/tinyforge/internal/store"
 )
 
+// signatureHeader is the canonical Gitea/GitHub-compatible header name for
+// HMAC-SHA256 signatures over the raw request body. Tinyforge accepts the
+// same header so existing CI integrations work unchanged.
+const signatureHeader = "X-Hub-Signature-256"
+
+// verifyHMAC validates the X-Hub-Signature-256 header against the raw body
+// using HMAC-SHA256. The function does the comparison in constant time.
+//
+// Behavior:
+//   - signingSecret == "": signing not configured for this entity. The
+//     function returns (false, false) — the caller decides whether to
+//     enforce based on the require_signature flag.
+//   - header missing: returns (false, true) — caller-decided.
+//   - header malformed or signature mismatch: returns (false, true).
+//   - signature valid: returns (true, true).
+//
+// First return: whether the signature was successfully verified.
+// Second return: whether the verification was attempted (i.e., a header was
+// present or signing is configured). The caller uses this to distinguish
+// "no signature submitted" from "wrong signature submitted".
+func verifyHMAC(signingSecret string, body []byte, headerValue string) (verified, attempted bool) {
+	if signingSecret == "" {
+		return false, false
+	}
+	if headerValue == "" {
+		return false, false
+	}
+	const prefix = "sha256="
+	if !strings.HasPrefix(headerValue, prefix) {
+		return false, true
+	}
+	provided, err := hex.DecodeString(headerValue[len(prefix):])
+	if err != nil {
+		return false, true
+	}
+	mac := hmac.New(sha256.New, []byte(signingSecret))
+	mac.Write(body)
+	expected := mac.Sum(nil)
+	return hmac.Equal(provided, expected), true
+}
+
 // maxSiteConcurrentSyncs caps fan-out of background site syncs triggered by
 // webhooks. Above this limit, requests are rejected with 503.
 const maxSiteConcurrentSyncs = 4
@@ -217,9 +261,31 @@ func (h *Handler) handleWebhook(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Read body once so we can both verify HMAC and decode JSON.
+	body, err := io.ReadAll(io.LimitReader(r.Body, maxWebhookBodyBytes))
+	if err != nil {
+		respondWebhookError(w, http.StatusBadRequest, "failed to read request body")
+		return
+	}
+
+	// HMAC enforcement: a configured signing secret + the require_signature
+	// flag together produce a hard reject on missing/invalid signatures.
+	// When the flag is off we still verify any submitted signature so a
+	// CI misconfiguration surfaces as a 401 rather than silent acceptance.
+	verified, attempted := verifyHMAC(project.WebhookSigningSecret, body, r.Header.Get(signatureHeader))
+	if project.WebhookRequireSignature && !verified {
+		slog.Warn("webhook: signature required but invalid/missing", "project", project.Name)
+		respondWebhookError(w, http.StatusUnauthorized, "invalid or missing signature")
+		return
+	}
+	if attempted && !verified {
+		slog.Warn("webhook: bad signature", "project", project.Name)
+		respondWebhookError(w, http.StatusUnauthorized, "invalid signature")
+		return
+	}
+
 	var payload Payload
-	dec := json.NewDecoder(io.LimitReader(r.Body, maxWebhookBodyBytes))
-	if err := dec.Decode(&payload); err != nil {
+	if err := json.Unmarshal(body, &payload); err != nil {
 		respondWebhookError(w, http.StatusBadRequest, "invalid JSON payload")
 		return
 	}
@@ -347,6 +413,21 @@ func (h *Handler) handleSiteWebhook(w http.ResponseWriter, r *http.Request) {
 		respondWebhookError(w, http.StatusBadRequest, "failed to read request body")
 		return
 	}
+
+	// HMAC enforcement matches the project flow: hard reject when required,
+	// soft reject when an invalid signature is supplied without enforcement.
+	verified, attempted := verifyHMAC(site.WebhookSigningSecret, body, r.Header.Get(signatureHeader))
+	if site.WebhookRequireSignature && !verified {
+		slog.Warn("webhook: site signature required but invalid/missing", "site", site.Name)
+		respondWebhookError(w, http.StatusUnauthorized, "invalid or missing signature")
+		return
+	}
+	if attempted && !verified {
+		slog.Warn("webhook: site bad signature", "site", site.Name)
+		respondWebhookError(w, http.StatusUnauthorized, "invalid signature")
+		return
+	}
+
 	if len(body) > 0 {
 		if err := json.Unmarshal(body, &payload); err != nil {
 			respondWebhookError(w, http.StatusBadRequest, "invalid JSON payload")

internal/webhook/handler_test.go

@@ -2,6 +2,9 @@ package webhook_test
 
 import (
 	"context"
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/hex"
 	"encoding/json"
 	"io"
 	"net/http"
@@ -16,6 +19,29 @@ import (
 	"github.com/alexei/tinyforge/internal/webhook"
 )
 
+// signBody computes the HMAC-SHA256 hex digest used by the X-Hub-Signature-256 header.
+func signBody(secret, body string) string {
+	mac := hmac.New(sha256.New, []byte(secret))
+	mac.Write([]byte(body))
+	return "sha256=" + hex.EncodeToString(mac.Sum(nil))
+}
+
+// doJSONSigned mirrors doJSON but adds the X-Hub-Signature-256 header.
+func doJSONSigned(t *testing.T, r chi.Router, method, path, body, signingSecret string) (*http.Response, string) {
+	t.Helper()
+	req := httptest.NewRequest(method, path, strings.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	if signingSecret != "" {
+		req.Header.Set("X-Hub-Signature-256", signBody(signingSecret, body))
+	}
+	w := httptest.NewRecorder()
+	r.ServeHTTP(w, req)
+	resp := w.Result()
+	b, _ := io.ReadAll(resp.Body)
+	resp.Body.Close()
+	return resp, string(b)
+}
+
 // fakeDeployer records the last trigger for assertion.
 type fakeDeployer struct {
 	mu       sync.Mutex
@@ -309,3 +335,123 @@ func TestSiteWebhook_PushSkippedForNonMatchingBranch(t *testing.T) {
 		t.Errorf("non-matching branch must not trigger sync; got %d calls", ft.calls)
 	}
 }
+
+// HMAC enforcement scenarios.
+
+func TestProjectWebhook_HMACRequiredAndValid(t *testing.T) {
+	t.Parallel()
+	st := newStore(t)
+	p, _ := st.CreateProject(store.Project{
+		Name: "app", Image: "alexei/app", Env: "{}", Volumes: "{}",
+	})
+	if _, err := st.CreateStage(store.Stage{
+		ProjectID: p.ID, Name: "dev", TagPattern: "*", AutoDeploy: true, MaxInstances: 1,
+	}); err != nil {
+		t.Fatal(err)
+	}
+	const sig = "deadbeef-signing-secret-1234567890abcdef"
+	if err := st.SetProjectWebhookSigningSecret(p.ID, sig); err != nil {
+		t.Fatal(err)
+	}
+	if err := st.SetProjectWebhookRequireSignature(p.ID, true); err != nil {
+		t.Fatal(err)
+	}
+
+	dep := &fakeDeployer{}
+	h := webhook.NewHandler(st, dep, nil)
+	r := newRouter(t, h)
+
+	body := `{"image":"alexei/app:dev-abc"}`
+	resp, msg := doJSONSigned(t, r, http.MethodPost, "/api/webhook/"+p.WebhookSecret, body, sig)
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("expected 200 with valid sig, got %d: %s", resp.StatusCode, msg)
+	}
+	if dep.calls != 1 {
+		t.Errorf("valid signed deploy should fire once, got %d", dep.calls)
+	}
+}
+
+func TestProjectWebhook_HMACRequiredButMissing(t *testing.T) {
+	t.Parallel()
+	st := newStore(t)
+	p, _ := st.CreateProject(store.Project{
+		Name: "app", Image: "alexei/app", Env: "{}", Volumes: "{}",
+	})
+	if _, err := st.CreateStage(store.Stage{
+		ProjectID: p.ID, Name: "dev", TagPattern: "*", AutoDeploy: true, MaxInstances: 1,
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if err := st.SetProjectWebhookSigningSecret(p.ID, "abc-signing-secret-12345678901234567890"); err != nil {
+		t.Fatal(err)
+	}
+	if err := st.SetProjectWebhookRequireSignature(p.ID, true); err != nil {
+		t.Fatal(err)
+	}
+
+	dep := &fakeDeployer{}
+	h := webhook.NewHandler(st, dep, nil)
+	r := newRouter(t, h)
+
+	resp, _ := doJSON(t, r, http.MethodPost, "/api/webhook/"+p.WebhookSecret, `{"image":"alexei/app:dev-abc"}`)
+	if resp.StatusCode != http.StatusUnauthorized {
+		t.Fatalf("missing signature must return 401 when required, got %d", resp.StatusCode)
+	}
+	if dep.calls != 0 {
+		t.Errorf("deploy must not fire when required signature is missing")
+	}
+}
+
+func TestProjectWebhook_HMACPresentButWrong(t *testing.T) {
+	t.Parallel()
+	st := newStore(t)
+	p, _ := st.CreateProject(store.Project{
+		Name: "app", Image: "alexei/app", Env: "{}", Volumes: "{}",
+	})
+	if _, err := st.CreateStage(store.Stage{
+		ProjectID: p.ID, Name: "dev", TagPattern: "*", AutoDeploy: true, MaxInstances: 1,
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if err := st.SetProjectWebhookSigningSecret(p.ID, "real-signing-secret-1234567890abcdef"); err != nil {
+		t.Fatal(err)
+	}
+	// Note: require_signature stays false — but a wrong sig must still 401.
+
+	dep := &fakeDeployer{}
+	h := webhook.NewHandler(st, dep, nil)
+	r := newRouter(t, h)
+
+	resp, _ := doJSONSigned(t, r, http.MethodPost, "/api/webhook/"+p.WebhookSecret,
+		`{"image":"alexei/app:dev-abc"}`, "wrong-secret-xxxxxxxxxxxxxxxxxxxxxxxxxxxx")
+	if resp.StatusCode != http.StatusUnauthorized {
+		t.Fatalf("wrong signature must 401, got %d", resp.StatusCode)
+	}
+	if dep.calls != 0 {
+		t.Errorf("deploy must not fire on wrong signature")
+	}
+}
+
+func TestProjectWebhook_HMACOptionalUnsignedAccepted(t *testing.T) {
+	// require_signature=false AND signing_secret="": unsigned requests pass.
+	t.Parallel()
+	st := newStore(t)
+	p, _ := st.CreateProject(store.Project{
+		Name: "app", Image: "alexei/app", Env: "{}", Volumes: "{}",
+	})
+	if _, err := st.CreateStage(store.Stage{
+		ProjectID: p.ID, Name: "dev", TagPattern: "*", AutoDeploy: true, MaxInstances: 1,
+	}); err != nil {
+		t.Fatal(err)
+	}
+	dep := &fakeDeployer{}
+	h := webhook.NewHandler(st, dep, nil)
+	r := newRouter(t, h)
+	resp, _ := doJSON(t, r, http.MethodPost, "/api/webhook/"+p.WebhookSecret, `{"image":"alexei/app:dev-x"}`)
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("unsigned + unconfigured should pass, got %d", resp.StatusCode)
+	}
+	if dep.calls != 1 {
+		t.Errorf("expected 1 deploy, got %d", dep.calls)
+	}
+}