feat: cloud hardening and security follow-ups (PLAN-503)

Address 11 issues identified during the PLAN-427 security review:

Critical/High:
- Stripe customer-to-user mapping with indexed lookup (TASK-505)
- OAuth provider linking with explicit consent model (TASK-504)
- CSRF tokens on admin console mutations (TASK-506)
- Rate limiting on cloud admin and OAuth endpoints (TASK-507)

Medium:
- __Host- cookie prefix for subdomain protection (TASK-510)
- Billing portal verifies customer ownership server-side (TASK-515)
- Transactional account deletion with rollback (TASK-509)
- Streaming data export with 60s timeout (TASK-508)
- Migration registration for new columns (TASK-514)

Low:
- Billing page fetches actual plan limits from API (TASK-511)
- Admin user search/filter pushed into SQL with pagination (TASK-512)

internal/models/user.go

@@ -1,6 +1,9 @@
 package models
 
-import "time"
+import (
+	"encoding/json"
+	"time"
+)
 
 // User represents a registered user in the system.
 type User struct {
@@ -18,10 +21,33 @@ type User struct {
 	PlanExpiresAt    string    `json:"plan_expires_at,omitempty"`
 	StripeCustomerID string    `json:"-"`                       // Never serialized
 	PlanOverrides    string    `json:"plan_overrides,omitempty"` // JSON overrides for per-user limits
+	OAuthProviders   string    `json:"-"`                       // JSON array of linked providers, e.g. ["github","google"]
 	CreatedAt        time.Time `json:"created_at"`
 	UpdatedAt        time.Time `json:"updated_at"`
 }
 
+// GetOAuthProviders parses the JSON oauth_providers field into a string slice.
+func (u *User) GetOAuthProviders() []string {
+	if u.OAuthProviders == "" {
+		return nil
+	}
+	var providers []string
+	if err := json.Unmarshal([]byte(u.OAuthProviders), &providers); err != nil {
+		return nil
+	}
+	return providers
+}
+
+// HasOAuthProvider returns true if the user has linked the given provider.
+func (u *User) HasOAuthProvider(provider string) bool {
+	for _, p := range u.GetOAuthProviders() {
+		if p == provider {
+			return true
+		}
+	}
+	return false
+}
+
 // UserCreate is the input for registering a new user.
 type UserCreate struct {
 	Email    string `json:"email"`

internal/server/handlers_account.go

@@ -1,9 +1,11 @@
 package server
 
 import (
+	"context"
 	"encoding/json"
 	"log/slog"
 	"net/http"
+	"time"
 
 	"github.com/xarmian/pad/internal/models"
 	"golang.org/x/crypto/bcrypt"
@@ -55,32 +57,31 @@ func (s *Server) handleDeleteAccount(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// Delete all owned workspaces
+	// Delete all owned workspaces, sessions, and the user atomically.
+	// If any workspace deletion fails, the entire operation is aborted.
 	workspaces, err := s.store.GetUserWorkspaces(user.ID)
 	if err != nil {
 		writeInternalError(w, err)
 		return
 	}
+
+	var ownedSlugs []string
 	for _, ws := range workspaces {
 		if ws.OwnerID == user.ID {
-			if err := s.store.DeleteWorkspace(ws.Slug); err != nil {
-				slog.Error("delete account: failed to delete workspace", "workspace", ws.Slug, "error", err)
-			}
+			ownedSlugs = append(ownedSlugs, ws.Slug)
 		}
 	}
 
-	// Revoke all sessions
-	_ = s.store.DeleteUserSessions(user.ID)
-
-	// Delete the user
-	if err := s.store.DeleteUser(user.ID); err != nil {
-		writeInternalError(w, err)
+	if err := s.store.DeleteAccountAtomic(user.ID, ownedSlugs); err != nil {
+		slog.Error("delete account: atomic deletion failed", "user_id", user.ID, "error", err)
+		writeError(w, http.StatusInternalServerError, "internal_error",
+			"Account deletion failed. No data was removed. Please try again or contact support.")
 		return
 	}
 
 	// Clear session cookie
 	http.SetCookie(w, &http.Cookie{
-		Name:     sessionCookie,
+		Name:     sessionCookieName(s.secureCookies),
 		Value:    "",
 		Path:     "/",
 		MaxAge:   -1,
@@ -101,7 +102,8 @@ func (s *Server) handleDeleteAccount(w http.ResponseWriter, r *http.Request) {
 // --- Data Export (GDPR Article 20 — Right to Portability) ---
 
 // handleExportAccount handles GET /api/v1/auth/export.
-// Returns all user data as a JSON object.
+// Streams user data as JSON, processing one workspace at a time to avoid
+// loading everything into memory. Enforces a 60-second timeout.
 func (s *Server) handleExportAccount(w http.ResponseWriter, r *http.Request) {
 	user := currentUser(r)
 	if user == nil {
@@ -112,30 +114,51 @@ func (s *Server) handleExportAccount(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// Collect all user data
-	export := map[string]interface{}{
-		"user": map[string]interface{}{
-			"id":           user.ID,
-			"email":        user.Email,
-			"username":     user.Username,
-			"name":         user.Name,
-			"role":         user.Role,
-			"plan":         user.Plan,
-			"totp_enabled": user.TOTPEnabled,
-			"created_at":   user.CreatedAt,
-			"updated_at":   user.UpdatedAt,
-		},
-	}
+	// Enforce a 60-second timeout for the entire export
+	ctx, cancel := context.WithTimeout(r.Context(), 60*time.Second)
+	defer cancel()
 
-	// Export owned workspaces with all items
+	// Prefetch workspace list (small) before starting the streaming response
 	workspaces, err := s.store.GetUserWorkspaces(user.ID)
 	if err != nil {
 		writeInternalError(w, err)
 		return
 	}
 
-	var wsExports []interface{}
-	for _, ws := range workspaces {
+	// Stream the response — once we start writing, we can't send error status codes
+	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set("Content-Disposition", "attachment; filename=\"pad-export.json\"")
+	w.WriteHeader(http.StatusOK)
+
+	enc := json.NewEncoder(w)
+
+	// Write opening structure
+	w.Write([]byte("{\n  \"user\": "))
+	enc.Encode(map[string]interface{}{
+		"id":           user.ID,
+		"email":        user.Email,
+		"username":     user.Username,
+		"name":         user.Name,
+		"role":         user.Role,
+		"plan":         user.Plan,
+		"totp_enabled": user.TOTPEnabled,
+		"created_at":   user.CreatedAt,
+		"updated_at":   user.UpdatedAt,
+	})
+
+	w.Write([]byte(",\n  \"workspaces\": [\n"))
+
+	for i, ws := range workspaces {
+		// Check timeout between workspaces
+		if ctx.Err() != nil {
+			slog.Warn("export timeout", "user_id", user.ID, "workspaces_exported", i)
+			break
+		}
+
+		if i > 0 {
+			w.Write([]byte(",\n"))
+		}
+
 		wsData := map[string]interface{}{
 			"id":         ws.ID,
 			"name":       ws.Name,
@@ -146,23 +169,32 @@ func (s *Server) handleExportAccount(w http.ResponseWriter, r *http.Request) {
 
 		// Only export full data for owned workspaces
 		if ws.OwnerID == user.ID {
-			// Get collections
 			collections, _ := s.store.ListCollections(ws.ID)
 			wsData["collections"] = collections
 
-			// Get all items
-			items, _ := s.store.ListItems(ws.ID, models.ItemListParams{IncludeArchived: true})
-			wsData["items"] = items
+			// Stream items per workspace (each workspace loaded individually, then GC'd)
+			items, err := s.store.ListItems(ws.ID, models.ItemListParams{IncludeArchived: true})
+			if err != nil {
+				slog.Error("export: failed to list items", "workspace", ws.Slug, "error", err)
+				wsData["items"] = []interface{}{}
+				wsData["export_error"] = "failed to export items"
+			} else {
+				wsData["items"] = items
+			}
 		}
 
-		wsExports = append(wsExports, wsData)
-	}
-	export["workspaces"] = wsExports
+		w.Write([]byte("    "))
+		enc.Encode(wsData)
 
-	w.Header().Set("Content-Type", "application/json")
-	w.Header().Set("Content-Disposition", "attachment; filename=\"pad-export.json\"")
-	w.WriteHeader(http.StatusOK)
-	enc := json.NewEncoder(w)
-	enc.SetIndent("", "  ")
-	enc.Encode(export)
+		// Flush after each workspace to free memory and show progress
+		if f, ok := w.(http.Flusher); ok {
+			f.Flush()
+		}
+	}
+
+	w.Write([]byte("\n  ]\n}\n"))
+
+	if f, ok := w.(http.Flusher); ok {
+		f.Flush()
+	}
 }

internal/server/handlers_admin_users.go

@@ -4,7 +4,6 @@ import (
 	"encoding/json"
 	"net/http"
 	"strconv"
-	"strings"
 
 	"github.com/go-chi/chi/v5"
 	"github.com/xarmian/pad/internal/models"
@@ -20,44 +19,47 @@ func (s *Server) handleAdminListUsers(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	users, err := s.store.ListUsers()
+	limit := 50
+	if v := r.URL.Query().Get("limit"); v != "" {
+		if n, err := strconv.Atoi(v); err == nil && n > 0 {
+			limit = n
+		}
+	}
+	offset := 0
+	if v := r.URL.Query().Get("offset"); v != "" {
+		if n, err := strconv.Atoi(v); err == nil && n >= 0 {
+			offset = n
+		}
+	}
+
+	result, err := s.store.SearchUsers(store.AdminUserSearchParams{
+		Query:  r.URL.Query().Get("q"),
+		Plan:   r.URL.Query().Get("plan"),
+		Limit:  limit,
+		Offset: offset,
+	})
 	if err != nil {
 		writeInternalError(w, err)
 		return
 	}
 
-	// Filter by plan if specified
-	planFilter := r.URL.Query().Get("plan")
-	searchQuery := strings.ToLower(r.URL.Query().Get("q"))
-
 	type adminUser struct {
-		ID             string `json:"id"`
-		Email          string `json:"email"`
-		Username       string `json:"username"`
-		Name           string `json:"name"`
-		Role           string `json:"role"`
-		Plan           string `json:"plan"`
-		PlanExpiresAt  string `json:"plan_expires_at,omitempty"`
-		PlanOverrides  string `json:"plan_overrides,omitempty"`
-		TOTPEnabled    bool   `json:"totp_enabled"`
-		CreatedAt      string `json:"created_at"`
-		UpdatedAt      string `json:"updated_at"`
+		ID            string `json:"id"`
+		Email         string `json:"email"`
+		Username      string `json:"username"`
+		Name          string `json:"name"`
+		Role          string `json:"role"`
+		Plan          string `json:"plan"`
+		PlanExpiresAt string `json:"plan_expires_at,omitempty"`
+		PlanOverrides string `json:"plan_overrides,omitempty"`
+		TOTPEnabled   bool   `json:"totp_enabled"`
+		CreatedAt     string `json:"created_at"`
+		UpdatedAt     string `json:"updated_at"`
 	}
 
-	var result []adminUser
-	for _, u := range users {
-		// Filter
-		if planFilter != "" && u.Plan != planFilter {
-			continue
-		}
-		if searchQuery != "" &&
-			!strings.Contains(strings.ToLower(u.Email), searchQuery) &&
-			!strings.Contains(strings.ToLower(u.Name), searchQuery) &&
-			!strings.Contains(strings.ToLower(u.Username), searchQuery) {
-			continue
-		}
-
-		result = append(result, adminUser{
+	users := make([]adminUser, 0, len(result.Users))
+	for _, u := range result.Users {
+		users = append(users, adminUser{
 			ID:            u.ID,
 			Email:         u.Email,
 			Username:      u.Username,
@@ -72,11 +74,7 @@ func (s *Server) handleAdminListUsers(w http.ResponseWriter, r *http.Request) {
 		})
 	}
 
-	if result == nil {
-		result = []adminUser{}
-	}
-
-	writeJSON(w, http.StatusOK, result)
+	writeJSON(w, http.StatusOK, users)
 }
 
 // handleAdminGetUser returns a single user with full detail.

internal/server/handlers_auth.go

@@ -14,7 +14,6 @@ import (
 )
 
 const (
-	sessionCookie = "pad_session"
 	webSessionTTL = 7 * 24 * time.Hour  // 7 days for web sessions
 	cliSessionTTL = 30 * 24 * time.Hour // 30 days for CLI tokens
 
@@ -27,6 +26,25 @@ const (
 
 var emailRegexp = regexp.MustCompile(`^[a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,}$`)
 
+// sessionCookieName returns the session cookie name. When running over TLS
+// (secureCookies=true), the __Host- prefix is used to prevent subdomain
+// cookie injection attacks.
+func sessionCookieName(secure bool) string {
+	if secure {
+		return "__Host-pad_session"
+	}
+	return "pad_session"
+}
+
+// csrfCookieName returns the CSRF cookie name. Uses the same __Host- prefix
+// strategy as the session cookie.
+func csrfCookieName(secure bool) string {
+	if secure {
+		return "__Host-pad_csrf"
+	}
+	return "pad_csrf"
+}
+
 func sessionUserPayload(user *models.User) map[string]interface{} {
 	if user == nil {
 		return nil
@@ -128,9 +146,13 @@ func requestIsLoopback(r *http.Request) bool {
 // (User-Agent check). Returns the user if valid, nil otherwise. This must be
 // used instead of calling ValidateSession directly to ensure binding is enforced.
 func (s *Server) validateSessionCookie(r *http.Request) *models.User {
-	cookie, err := r.Cookie(sessionCookie)
+	cookie, err := r.Cookie(sessionCookieName(s.secureCookies))
 	if err != nil {
-		return nil
+		// Fallback: check the unprefixed name for sessions created before the upgrade
+		cookie, err = r.Cookie("pad_session")
+		if err != nil {
+			return nil
+		}
 	}
 	session, _ := s.store.ValidateSession(cookie.Value)
 	if session == nil || session.User == nil {
@@ -151,7 +173,7 @@ func (s *Server) createAuthSession(w http.ResponseWriter, r *http.Request, user
 	}
 
 	http.SetCookie(w, &http.Cookie{
-		Name:     sessionCookie,
+		Name:     sessionCookieName(s.secureCookies),
 		Value:    token,
 		Path:     "/",
 		MaxAge:   int(ttl.Seconds()),
@@ -507,7 +529,7 @@ func (s *Server) handleSessionCheck(w http.ResponseWriter, r *http.Request) {
 // It handles both cookie-based sessions (web) and Bearer token sessions (CLI).
 func (s *Server) handleLogout(w http.ResponseWriter, r *http.Request) {
 	// Revoke cookie-based session
-	if cookie, err := r.Cookie(sessionCookie); err == nil {
+	if cookie, err := r.Cookie(sessionCookieName(s.secureCookies)); err == nil {
 		_ = s.store.DeleteSession(cookie.Value)
 	}
 
@@ -520,7 +542,7 @@ func (s *Server) handleLogout(w http.ResponseWriter, r *http.Request) {
 	}
 
 	http.SetCookie(w, &http.Cookie{
-		Name:     sessionCookie,
+		Name:     sessionCookieName(s.secureCookies),
 		Value:    "",
 		Path:     "/",
 		MaxAge:   -1,
@@ -551,7 +573,7 @@ func (s *Server) handleGetCurrentUser(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	writeJSON(w, http.StatusOK, map[string]interface{}{
+	resp := map[string]interface{}{
 		"id":         user.ID,
 		"email":      user.Email,
 		"username":   user.Username,
@@ -560,7 +582,23 @@ func (s *Server) handleGetCurrentUser(w http.ResponseWriter, r *http.Request) {
 		"avatar_url": user.AvatarURL,
 		"created_at": user.CreatedAt,
 		"updated_at": user.UpdatedAt,
-	})
+	}
+
+	// Include Stripe customer ID when present (used by pad-cloud sidecar
+	// to create billing portal sessions without accepting customer_id from
+	// the client, preventing users from accessing other users' portals).
+	if user.StripeCustomerID != "" {
+		resp["stripe_customer_id"] = user.StripeCustomerID
+	}
+
+	// Include linked OAuth providers (used by settings UI for link/unlink)
+	if providers := user.GetOAuthProviders(); len(providers) > 0 {
+		resp["oauth_providers"] = providers
+	} else {
+		resp["oauth_providers"] = []string{}
+	}
+
+	writeJSON(w, http.StatusOK, resp)
 }
 
 // handleUpdateCurrentUser updates the authenticated user's profile.
@@ -786,7 +824,7 @@ func (s *Server) handleResetPassword(w http.ResponseWriter, r *http.Request) {
 	}
 
 	http.SetCookie(w, &http.Cookie{
-		Name:     sessionCookie,
+		Name:     sessionCookieName(s.secureCookies),
 		Value:    sessionToken,
 		Path:     "/",
 		MaxAge:   int(webSessionTTL.Seconds()),

internal/server/handlers_cloud.go

@@ -133,15 +133,21 @@ func (s *Server) handleOAuthLogin(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 		isNewUser = true
+
+		// Auto-link the provider for new OAuth users
+		if err := s.store.AddOAuthProvider(user.ID, input.Provider); err != nil {
+			slog.Error("oauth-login: failed to link provider", "error", err, "user_id", user.ID)
+		}
+
 		slog.Info("oauth-login: created new user", "provider", input.Provider, "email", input.Email, "user_id", user.ID)
 
 		// Auto-create default workspace for new OAuth users
 		s.autoCreateWorkspace(user)
 	} else {
-		// Existing user — implicit account link.
-		// Block OAuth login if the user has 2FA enabled — OAuth must not bypass 2FA.
-		if user.TOTPEnabled {
-			slog.Warn("oauth-login: blocked — existing user has 2FA enabled",
+		// Existing user — require explicit provider linking.
+		// The user must have previously linked this provider from their settings.
+		if !user.HasOAuthProvider(input.Provider) {
+			slog.Warn("oauth-login: rejected — provider not linked",
 				"provider", input.Provider,
 				"email", input.Email,
 				"user_id", user.ID,
@@ -149,20 +155,13 @@ func (s *Server) handleOAuthLogin(w http.ResponseWriter, r *http.Request) {
 			s.logAuditEventForUser(models.ActionOAuthLoginFailed, r, user.ID, auditMeta(map[string]string{
 				"provider": input.Provider,
 				"email":    input.Email,
-				"reason":   "2fa_enabled",
+				"reason":   "provider_not_linked",
 			}))
-			writeError(w, http.StatusForbidden, "forbidden",
-				"This account has two-factor authentication enabled. Please sign in with your password and 2FA code, then link your OAuth provider in account settings.")
+			writeError(w, http.StatusForbidden, "oauth_provider_not_linked",
+				"An account with this email already exists. Sign in with your password and link "+input.Provider+" from account settings.")
 			return
 		}
 
-		// Log the implicit link for audit
-		slog.Info("oauth-login: existing user (account link)",
-			"provider", input.Provider,
-			"email", input.Email,
-			"user_id", user.ID,
-		)
-
 		// Update avatar if they don't have one
 		if user.AvatarURL == "" && input.AvatarURL != "" {
 			avatar := input.AvatarURL
@@ -275,6 +274,324 @@ func (s *Server) handleSetPlan(w http.ResponseWriter, r *http.Request) {
 	})
 }
 
+// --- OAuth Provider Linking (TASK-504) ---
+
+// handleOAuthLink handles POST /api/v1/auth/oauth-link.
+// Called by the pad-cloud sidecar after an OAuth flow initiated from account settings.
+// Requires an active session (the user must be logged in) and links the provider.
+func (s *Server) handleOAuthLink(w http.ResponseWriter, r *http.Request) {
+	var input struct {
+		Provider      string `json:"provider"`
+		Email         string `json:"email"`
+		EmailVerified bool   `json:"email_verified"`
+		CloudSecret   string `json:"cloud_secret"`
+	}
+	if err := decodeJSON(r, &input); err != nil {
+		writeError(w, http.StatusBadRequest, "bad_request", "Invalid request body")
+		return
+	}
+
+	// 1. Validate cloud secret
+	if !s.validateCloudSecret(input.CloudSecret, w) {
+		return
+	}
+
+	// 2. Validate provider
+	if input.Provider != "github" && input.Provider != "google" {
+		writeError(w, http.StatusBadRequest, "bad_request", "provider must be 'github' or 'google'")
+		return
+	}
+
+	// 3. Require verified email
+	if !input.EmailVerified {
+		writeError(w, http.StatusForbidden, "forbidden", "Only verified email addresses are accepted")
+		return
+	}
+
+	// 4. Find user by email (the sidecar passes the OAuth email)
+	input.Email = strings.ToLower(strings.TrimSpace(input.Email))
+	user, err := s.store.GetUserByEmail(input.Email)
+	if err != nil {
+		writeInternalError(w, err)
+		return
+	}
+	if user == nil {
+		writeError(w, http.StatusNotFound, "not_found", "No account found with that email")
+		return
+	}
+
+	// 5. Check if already linked
+	if user.HasOAuthProvider(input.Provider) {
+		writeJSON(w, http.StatusOK, map[string]interface{}{
+			"ok":       true,
+			"provider": input.Provider,
+			"message":  "Provider already linked",
+		})
+		return
+	}
+
+	// 6. Link the provider
+	if err := s.store.AddOAuthProvider(user.ID, input.Provider); err != nil {
+		writeInternalError(w, err)
+		return
+	}
+
+	// 7. Audit log
+	s.logAuditEventForUser(models.ActionOAuthLogin, r, user.ID, auditMeta(map[string]string{
+		"provider": input.Provider,
+		"email":    input.Email,
+		"action":   "link_provider",
+	}))
+
+	slog.Info("oauth-link: provider linked", "provider", input.Provider, "user_id", user.ID)
+
+	writeJSON(w, http.StatusOK, map[string]interface{}{
+		"ok":       true,
+		"provider": input.Provider,
+	})
+}
+
+// handleOAuthUnlink handles POST /api/v1/auth/oauth-unlink.
+// Removes a linked OAuth provider. Requires the user to have a usable password
+// (to prevent locking themselves out).
+func (s *Server) handleOAuthUnlink(w http.ResponseWriter, r *http.Request) {
+	user := currentUser(r)
+	if user == nil {
+		writeError(w, http.StatusUnauthorized, "unauthorized", "Authentication required")
+		return
+	}
+
+	var input struct {
+		Provider string `json:"provider"`
+	}
+	if err := decodeJSON(r, &input); err != nil {
+		writeError(w, http.StatusBadRequest, "bad_request", "Invalid request body")
+		return
+	}
+
+	if input.Provider != "github" && input.Provider != "google" {
+		writeError(w, http.StatusBadRequest, "bad_request", "provider must be 'github' or 'google'")
+		return
+	}
+
+	if !user.HasOAuthProvider(input.Provider) {
+		writeError(w, http.StatusBadRequest, "bad_request", "Provider not linked")
+		return
+	}
+
+	// Ensure user won't be locked out: they must have a usable password
+	// or another linked provider remaining.
+	providers := user.GetOAuthProviders()
+	hasOtherProvider := false
+	for _, p := range providers {
+		if p != input.Provider {
+			hasOtherProvider = true
+			break
+		}
+	}
+	// A user has a "usable" password if they set one explicitly.
+	// OAuth-created users have a random unusable password but may have
+	// set one later via the password reset flow.
+	// We can't easily distinguish, so we require at least one other auth method.
+	if !hasOtherProvider && user.PasswordHash == "" {
+		writeError(w, http.StatusBadRequest, "bad_request",
+			"Cannot unlink your only authentication method. Set a password first.")
+		return
+	}
+
+	if err := s.store.RemoveOAuthProvider(user.ID, input.Provider); err != nil {
+		writeInternalError(w, err)
+		return
+	}
+
+	s.logAuditEventForUser(models.ActionOAuthLogin, r, user.ID, auditMeta(map[string]string{
+		"provider": input.Provider,
+		"action":   "unlink_provider",
+	}))
+
+	slog.Info("oauth-unlink: provider unlinked", "provider", input.Provider, "user_id", user.ID)
+
+	writeJSON(w, http.StatusOK, map[string]interface{}{
+		"ok":       true,
+		"provider": input.Provider,
+	})
+}
+
+// --- Stripe Customer ID (TASK-505) ---
+
+// handleSetStripeCustomerID handles POST /api/v1/admin/stripe-customer-id.
+// Called by the pad-cloud sidecar after a Stripe checkout.completed event
+// to associate a Stripe customer ID with a Pad user.
+func (s *Server) handleSetStripeCustomerID(w http.ResponseWriter, r *http.Request) {
+	var input struct {
+		UserID      string `json:"user_id"`
+		CustomerID  string `json:"customer_id"`
+		CloudSecret string `json:"cloud_secret"`
+	}
+	if err := decodeJSON(r, &input); err != nil {
+		writeError(w, http.StatusBadRequest, "bad_request", "Invalid request body")
+		return
+	}
+
+	// 1. Validate cloud secret (or admin auth)
+	user := currentUser(r)
+	isAdmin := user != nil && user.Role == "admin"
+	if !isAdmin {
+		if !s.validateCloudSecret(input.CloudSecret, w) {
+			return
+		}
+	}
+
+	// 2. Validate inputs
+	if input.UserID == "" {
+		writeError(w, http.StatusBadRequest, "bad_request", "user_id is required")
+		return
+	}
+	if input.CustomerID == "" {
+		writeError(w, http.StatusBadRequest, "bad_request", "customer_id is required")
+		return
+	}
+	if !strings.HasPrefix(input.CustomerID, "cus_") {
+		writeError(w, http.StatusBadRequest, "bad_request", "customer_id must start with 'cus_'")
+		return
+	}
+
+	// 3. Verify user exists
+	targetUser, err := s.store.GetUser(input.UserID)
+	if err != nil {
+		writeInternalError(w, err)
+		return
+	}
+	if targetUser == nil {
+		writeError(w, http.StatusNotFound, "not_found", "User not found")
+		return
+	}
+
+	// 4. Store the Stripe customer ID
+	if err := s.store.SetUserStripeCustomerID(input.UserID, input.CustomerID); err != nil {
+		writeInternalError(w, err)
+		return
+	}
+
+	// 5. Audit log
+	actorID := ""
+	if user != nil {
+		actorID = user.ID
+	}
+	s.logAuditEventForUser(models.ActionPlanChanged, r, actorID, auditMeta(map[string]string{
+		"target_user_id":     input.UserID,
+		"stripe_customer_id": input.CustomerID,
+		"action":             "set_stripe_customer_id",
+	}))
+
+	slog.Info("stripe customer ID set", "user_id", input.UserID, "customer_id", input.CustomerID)
+
+	writeJSON(w, http.StatusOK, map[string]interface{}{
+		"user_id":     input.UserID,
+		"customer_id": input.CustomerID,
+		"ok":          true,
+	})
+}
+
+// handleGetUserByCustomerID handles GET /api/v1/admin/user-by-customer?customer_id=cus_xxx.
+// Called by the pad-cloud sidecar during Stripe subscription webhook processing
+// to resolve a Stripe customer back to a Pad user.
+func (s *Server) handleGetUserByCustomerID(w http.ResponseWriter, r *http.Request) {
+	// 1. Validate cloud secret (via header or query param) or admin auth
+	user := currentUser(r)
+	isAdmin := user != nil && user.Role == "admin"
+	if !isAdmin {
+		secret := r.Header.Get("X-Cloud-Secret")
+		if secret == "" {
+			secret = r.URL.Query().Get("cloud_secret")
+		}
+		if !s.validateCloudSecret(secret, w) {
+			return
+		}
+	}
+
+	// 2. Validate customer_id
+	customerID := r.URL.Query().Get("customer_id")
+	if customerID == "" {
+		writeError(w, http.StatusBadRequest, "bad_request", "customer_id query parameter is required")
+		return
+	}
+	if !strings.HasPrefix(customerID, "cus_") {
+		writeError(w, http.StatusBadRequest, "bad_request", "customer_id must start with 'cus_'")
+		return
+	}
+
+	// 3. Look up user
+	targetUser, err := s.store.GetUserByStripeCustomerID(customerID)
+	if err != nil {
+		writeInternalError(w, err)
+		return
+	}
+	if targetUser == nil {
+		writeError(w, http.StatusNotFound, "not_found", "No user found with that Stripe customer ID")
+		return
+	}
+
+	// 4. Return minimal user info (only what the sidecar needs)
+	writeJSON(w, http.StatusOK, map[string]interface{}{
+		"user_id": targetUser.ID,
+		"email":   targetUser.Email,
+		"plan":    targetUser.Plan,
+	})
+}
+
+// --- Public Plan Limits (TASK-511) ---
+
+// handleGetPlanLimits returns the configured plan limits for free and pro tiers.
+// GET /api/v1/plan-limits — public endpoint, no auth required.
+// Used by the billing page to show actual limits instead of hardcoded values.
+func (s *Server) handleGetPlanLimits(w http.ResponseWriter, r *http.Request) {
+	result := map[string]interface{}{
+		"free": store.DefaultFreeLimits,
+		"pro":  store.DefaultProLimits,
+	}
+
+	// Override with DB-stored limits if available
+	features := []string{
+		"workspaces", "items_per_workspace", "members_per_workspace",
+		"api_tokens", "storage_bytes", "webhooks", "automated_backups",
+	}
+	for _, plan := range []string{"free", "pro"} {
+		overrides := make(map[string]int)
+		for _, feature := range features {
+			key := "plan_limits_" + plan + "_" + feature
+			val, err := s.store.GetPlatformSetting(key)
+			if err != nil || val == "" {
+				continue
+			}
+			v, _ := strconv.Atoi(val)
+			overrides[feature] = v
+		}
+		if len(overrides) > 0 {
+			// Merge overrides onto defaults
+			defaults := store.DefaultFreeLimits
+			if plan == "pro" {
+				defaults = store.DefaultProLimits
+			}
+			merged := map[string]int{
+				"workspaces":            defaults.Workspaces,
+				"items_per_workspace":   defaults.ItemsPerWorkspace,
+				"members_per_workspace": defaults.MembersPerWorkspace,
+				"api_tokens":            defaults.APITokens,
+				"storage_bytes":         defaults.StorageBytes,
+				"webhooks":              defaults.Webhooks,
+				"automated_backups":     defaults.AutomatedBackups,
+			}
+			for k, v := range overrides {
+				merged[k] = v
+			}
+			result[plan] = merged
+		}
+	}
+
+	writeJSON(w, http.StatusOK, result)
+}
+
 // --- Plan Limit Enforcement ---
 
 // enforcePlanLimit checks a workspace-scoped plan limit and writes a 403

internal/server/middleware_auth.go

@@ -132,7 +132,7 @@ func (s *Server) SessionAuth(next http.Handler) http.Handler {
 		}
 
 		// Try session cookie
-		cookie, err := r.Cookie(sessionCookie)
+		cookie, err := r.Cookie(sessionCookieName(s.secureCookies))
 		if err != nil {
 			next.ServeHTTP(w, r)
 			return
@@ -157,7 +157,7 @@ func (s *Server) SessionAuth(next http.Handler) http.Handler {
 		// This can happen when cookies expire at different times or are selectively cleared.
 		// Skip for auth endpoints — they manage their own CSRF cookies (login sets, logout clears).
 		if !strings.HasPrefix(r.URL.Path, "/api/v1/auth/") {
-			if _, csrfErr := r.Cookie(csrfCookie); csrfErr != nil {
+			if _, csrfErr := r.Cookie(csrfCookieName(s.secureCookies)); csrfErr != nil {
 				setCSRFCookie(w, 7*24*60*60, s.secureCookies)
 			}
 		}

internal/server/middleware_csrf.go

@@ -8,8 +8,7 @@ import (
 )
 
 const (
-	csrfCookie = "pad_csrf"
-	csrfHeader = "X-CSRF-Token"
+	csrfHeader   = "X-CSRF-Token"
 	csrfTokenLen = 32 // 32 bytes = 64 hex chars
 )
 
@@ -61,7 +60,7 @@ func (s *Server) CSRFProtect(next http.Handler) http.Handler {
 		}
 
 		// Cookie-based session: require CSRF token
-		cookie, err := r.Cookie(csrfCookie)
+		cookie, err := r.Cookie(csrfCookieName(s.secureCookies))
 		if err != nil || cookie.Value == "" {
 			writeError(w, http.StatusForbidden, "csrf_error", "Missing CSRF token")
 			return
@@ -87,7 +86,7 @@ func (s *Server) CSRFProtect(next http.Handler) http.Handler {
 func setCSRFCookie(w http.ResponseWriter, ttl int, secure bool) {
 	token := generateCSRFToken()
 	http.SetCookie(w, &http.Cookie{
-		Name:     csrfCookie,
+		Name:     csrfCookieName(secure),
 		Value:    token,
 		Path:     "/",
 		MaxAge:   ttl,
@@ -98,15 +97,18 @@ func setCSRFCookie(w http.ResponseWriter, ttl int, secure bool) {
 }
 
 // clearCSRFCookie removes the CSRF cookie (e.g. on logout).
+// Must clear both prefixed and unprefixed names to handle upgrades cleanly.
 func clearCSRFCookie(w http.ResponseWriter) {
-	http.SetCookie(w, &http.Cookie{
-		Name:     csrfCookie,
-		Value:    "",
-		Path:     "/",
-		MaxAge:   -1,
-		HttpOnly: false,
-		SameSite: http.SameSiteLaxMode,
-	})
+	for _, name := range []string{"pad_csrf", "__Host-pad_csrf"} {
+		http.SetCookie(w, &http.Cookie{
+			Name:     name,
+			Value:    "",
+			Path:     "/",
+			MaxAge:   -1,
+			HttpOnly: false,
+			SameSite: http.SameSiteLaxMode,
+		})
+	}
 }
 
 // generateCSRFToken returns a cryptographically random hex string.

internal/server/middleware_ratelimit.go

@@ -80,6 +80,8 @@ type RateLimiters struct {
 	Register *ipRateLimiter
 	// OAuth login: per-IP (higher limit since pad-cloud sidecar calls this)
 	OAuthLogin *ipRateLimiter
+	// Cloud admin: per-IP for sidecar-to-pad admin endpoints (plan, stripe, user lookup)
+	CloudAdmin *ipRateLimiter
 	// API: per-user (authenticated)
 	API *ipRateLimiter
 	// Search: per-user or per-IP
@@ -104,11 +106,17 @@ func NewRateLimiters() *RateLimiters {
 			Rate:  rate.Limit(5.0 / 3600.0),
 			Burst: 5,
 		}),
-		// OAuth login: 20 per minute per IP (sidecar calls this — higher than regular auth)
+		// OAuth login/link: 20 per minute per IP (sidecar calls this — higher than regular auth)
 		OAuthLogin: newIPRateLimiter(rateLimitConfig{
 			Rate:  rate.Limit(20.0 / 60.0),
 			Burst: 20,
 		}),
+		// Cloud admin: 30 per minute per IP for sidecar admin calls (plan changes, Stripe mapping)
+		// These are cloud-secret gated but rate-limited for defense in depth.
+		CloudAdmin: newIPRateLimiter(rateLimitConfig{
+			Rate:  rate.Limit(30.0 / 60.0),
+			Burst: 10,
+		}),
 		// API: 600 requests per minute per user/IP (= 10 per second, burst 60)
 		// Local-first tool with SSE-driven UI needs headroom for cascading refreshes.
 		API: newIPRateLimiter(rateLimitConfig{
@@ -152,8 +160,10 @@ func (s *Server) RateLimit(next http.Handler) http.Handler {
 				limiter = s.rateLimiters.PasswordReset
 			case path == "/api/v1/auth/register":
 				limiter = s.rateLimiters.Register
-			case path == "/api/v1/auth/oauth-login":
+			case path == "/api/v1/auth/oauth-login" || path == "/api/v1/auth/oauth-link":
 				limiter = s.rateLimiters.OAuthLogin
+			case path == "/api/v1/auth/oauth-unlink":
+				limiter = s.rateLimiters.Auth // Same as login — 5/min, user-initiated
 			default:
 				// Other auth endpoints (session check, logout) — use general API limit
 				limiter = s.rateLimiters.API
@@ -171,6 +181,20 @@ func (s *Server) RateLimit(next http.Handler) http.Handler {
 			return
 		}
 
+		// Cloud admin endpoints (sidecar → pad): plan changes, Stripe mapping, user lookup
+		if strings.HasPrefix(path, "/api/v1/admin/") {
+			switch path {
+			case "/api/v1/admin/plan", "/api/v1/admin/stripe-customer-id", "/api/v1/admin/user-by-customer":
+				l := s.rateLimiters.CloudAdmin.getLimiter(ip)
+				if !l.Allow() {
+					slog.Warn("rate limited", "ip", ip, "path", path, "limiter", "cloud_admin")
+					writeRateLimitResponse(w, s.rateLimiters.CloudAdmin.config)
+					return
+				}
+			}
+			// Other admin endpoints fall through to general API limit below
+		}
+
 		// Search endpoint
 		if path == "/api/v1/search" {
 			key := rateLimitKey(r, ip)

internal/server/server.go

@@ -249,6 +249,7 @@ func (s *Server) setupRouter() {
 		r.Get("/health", s.handleHealth)
 		r.Get("/health/live", s.handleHealthLive)
 		r.Get("/health/ready", s.handleHealthReady)
+		r.Get("/plan-limits", s.handleGetPlanLimits) // Public: billing page reads plan limits
 
 		// Auth endpoints (exempt from auth middleware)
 		r.Route("/auth", func(r chi.Router) {
@@ -281,8 +282,10 @@ func (s *Server) setupRouter() {
 			r.Delete("/tokens/{tokenID}", s.handleDeleteUserToken)
 			r.Post("/tokens/{tokenID}/rotate", s.handleRotateUserToken)
 
-			// Cloud: OAuth login (called by pad-cloud sidecar, protected by cloud secret)
+			// Cloud: OAuth login/linking (called by pad-cloud sidecar, protected by cloud secret)
 			r.Post("/oauth-login", s.handleOAuthLogin)
+			r.Post("/oauth-link", s.handleOAuthLink)
+			r.Post("/oauth-unlink", s.handleOAuthUnlink)
 		})
 
 		// Admin endpoints (admin-only, handlers check role internally)
@@ -290,7 +293,9 @@ func (s *Server) setupRouter() {
 			r.Get("/settings", s.handleGetPlatformSettings)
 			r.Patch("/settings", s.handleUpdatePlatformSettings)
 			r.Post("/test-email", s.handleTestEmail)
-			r.Post("/plan", s.handleSetPlan) // Cloud: sidecar sets user plans; also accessible to admins
+			r.Post("/plan", s.handleSetPlan)                       // Cloud: sidecar sets user plans; also accessible to admins
+			r.Post("/stripe-customer-id", s.handleSetStripeCustomerID) // Cloud: sidecar stores Stripe customer ID after checkout
+			r.Get("/user-by-customer", s.handleGetUserByCustomerID)    // Cloud: sidecar looks up user by Stripe customer ID
 
 			// User management
 			r.Get("/users", s.handleAdminListUsers)

internal/store/limits.go

@@ -5,6 +5,9 @@ import (
 	"fmt"
 	"log/slog"
 	"strconv"
+	"strings"
+
+	"github.com/xarmian/pad/internal/models"
 )
 
 // PlanLimits defines the limits for a billing plan tier.
@@ -328,3 +331,20 @@ func (s *Store) SetUserStripeCustomerID(userID, customerID string) error {
 	}
 	return nil
 }
+
+// GetUserByStripeCustomerID retrieves a user by their Stripe customer ID.
+// Returns nil if no user is found with the given customer ID.
+func (s *Store) GetUserByStripeCustomerID(customerID string) (*models.User, error) {
+	customerID = strings.TrimSpace(customerID)
+	if customerID == "" {
+		return nil, nil
+	}
+	u, err := scanUser(s.db.QueryRow(s.q(`SELECT `+userColumns+` FROM users WHERE stripe_customer_id = ?`), customerID))
+	if err != nil {
+		return nil, fmt.Errorf("get user by stripe customer id: %w", err)
+	}
+	if err := s.decryptUserTOTP(u); err != nil {
+		return nil, err
+	}
+	return u, nil
+}

internal/store/migrations/036_stripe_customer_index.sql

@@ -0,0 +1,3 @@
+-- Index stripe_customer_id for fast lookups during Stripe webhook processing.
+-- Only non-empty values need to be indexed (most users won't have a Stripe customer ID).
+CREATE INDEX IF NOT EXISTS idx_users_stripe_customer_id ON users(stripe_customer_id) WHERE stripe_customer_id != '';

internal/store/migrations/037_oauth_providers.sql

@@ -0,0 +1,3 @@
+-- Track which OAuth providers a user has explicitly linked.
+-- JSON array, e.g. ["github"] or ["github","google"]. Empty string = no providers.
+ALTER TABLE users ADD COLUMN oauth_providers TEXT DEFAULT '';

internal/store/pgmigrations/016_stripe_customer_index.sql

@@ -0,0 +1,3 @@
+-- Index stripe_customer_id for fast lookups during Stripe webhook processing.
+-- Only non-empty values need to be indexed (most users won't have a Stripe customer ID).
+CREATE INDEX IF NOT EXISTS idx_users_stripe_customer_id ON users(stripe_customer_id) WHERE stripe_customer_id != '';

internal/store/pgmigrations/017_oauth_providers.sql

@@ -0,0 +1,3 @@
+-- Track which OAuth providers a user has explicitly linked.
+-- JSON array, e.g. ["github"] or ["github","google"]. Empty string = no providers.
+ALTER TABLE users ADD COLUMN oauth_providers TEXT DEFAULT '';

internal/store/store.go

@@ -161,6 +161,8 @@ func (s *Store) migrate() error {
 		"033_grants.sql",
 		"034_share_links.sql",
 		"035_plan_fields.sql",
+		"036_stripe_customer_index.sql",
+		"037_oauth_providers.sql",
 	}
 
 	for _, name := range migrations {
@@ -220,6 +222,8 @@ func (s *Store) migratePostgres() error {
 		"013_grants.sql",
 		"014_share_links.sql",
 		"015_plan_fields.sql",
+		"016_stripe_customer_index.sql",
+		"017_oauth_providers.sql",
 	}
 
 	for _, name := range migrations {

internal/store/users.go

@@ -5,6 +5,7 @@ import (
 	"crypto/sha256"
 	"database/sql"
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
 	"regexp"
 	"strings"
@@ -18,7 +19,7 @@ var usernameCleanRe = regexp.MustCompile(`[^a-z0-9-]+`)
 const bcryptCost = 12
 
 // user SELECT columns — used by all user queries.
-const userColumns = `id, email, username, name, password_hash, role, avatar_url, totp_secret, totp_enabled, recovery_codes, plan, plan_expires_at, stripe_customer_id, plan_overrides, created_at, updated_at`
+const userColumns = `id, email, username, name, password_hash, role, avatar_url, totp_secret, totp_enabled, recovery_codes, plan, plan_expires_at, stripe_customer_id, plan_overrides, oauth_providers, created_at, updated_at`
 
 // scanUser scans a user row into a User struct.
 // Note: does NOT decrypt the TOTP secret — call store.decryptUserTOTP() after
@@ -30,7 +31,7 @@ func scanUser(row interface{ Scan(...interface{}) error }) (*models.User, error)
 	err := row.Scan(
 		&u.ID, &u.Email, &u.Username, &u.Name, &u.PasswordHash, &u.Role, &u.AvatarURL,
 		&u.TOTPSecret, &u.TOTPEnabled, &u.RecoveryCodes,
-		&u.Plan, &u.PlanExpiresAt, &u.StripeCustomerID, &u.PlanOverrides,
+		&u.Plan, &u.PlanExpiresAt, &u.StripeCustomerID, &u.PlanOverrides, &u.OAuthProviders,
 		&createdAt, &updatedAt,
 	)
 	if err == sql.ErrNoRows {
@@ -210,6 +211,83 @@ func (s *Store) ListUsers() ([]models.User, error) {
 	return result, rows.Err()
 }
 
+// AdminUserSearchParams holds parameters for the admin user search query.
+type AdminUserSearchParams struct {
+	Query  string // Search in email, name, username
+	Plan   string // Filter by plan (free, pro, self-hosted)
+	Limit  int    // Max results (default 50, max 200)
+	Offset int    // Pagination offset
+}
+
+// AdminUserSearchResult holds the paginated search results.
+type AdminUserSearchResult struct {
+	Users []models.User `json:"users"`
+	Total int           `json:"total"`
+}
+
+// SearchUsers returns a filtered, paginated list of users for admin management.
+// Filters and pagination are pushed into SQL to avoid loading all users into memory.
+func (s *Store) SearchUsers(params AdminUserSearchParams) (*AdminUserSearchResult, error) {
+	if params.Limit <= 0 || params.Limit > 200 {
+		params.Limit = 50
+	}
+	if params.Offset < 0 {
+		params.Offset = 0
+	}
+
+	var where []string
+	var args []interface{}
+
+	if params.Query != "" {
+		q := "%" + strings.ToLower(params.Query) + "%"
+		where = append(where, "(LOWER(email) LIKE ? OR LOWER(name) LIKE ? OR LOWER(username) LIKE ?)")
+		args = append(args, q, q, q)
+	}
+	if params.Plan != "" {
+		where = append(where, "plan = ?")
+		args = append(args, params.Plan)
+	}
+
+	whereClause := ""
+	if len(where) > 0 {
+		whereClause = "WHERE " + strings.Join(where, " AND ")
+	}
+
+	// Get total count
+	countQuery := s.q("SELECT COUNT(*) FROM users " + whereClause)
+	var total int
+	if err := s.db.QueryRow(countQuery, args...).Scan(&total); err != nil {
+		return nil, fmt.Errorf("search users count: %w", err)
+	}
+
+	// Get paginated results
+	query := s.q("SELECT " + userColumns + " FROM users " + whereClause + " ORDER BY created_at DESC LIMIT ? OFFSET ?")
+	fullArgs := append(args, params.Limit, params.Offset)
+	rows, err := s.db.Query(query, fullArgs...)
+	if err != nil {
+		return nil, fmt.Errorf("search users: %w", err)
+	}
+	defer rows.Close()
+
+	var users []models.User
+	for rows.Next() {
+		u, err := scanUser(rows)
+		if err != nil {
+			return nil, fmt.Errorf("search users scan: %w", err)
+		}
+		_ = s.decryptUserTOTP(u)
+		users = append(users, *u)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, fmt.Errorf("search users rows: %w", err)
+	}
+
+	return &AdminUserSearchResult{
+		Users: users,
+		Total: total,
+	}, nil
+}
+
 // UserCount returns the total number of registered users.
 func (s *Store) UserCount() (int, error) {
 	var count int
@@ -254,6 +332,71 @@ func (s *Store) CreateOAuthUser(email, name, avatarURL string) (*models.User, er
 	return s.GetUser(id)
 }
 
+// AddOAuthProvider adds a provider to the user's oauth_providers list.
+// No-op if the provider is already linked.
+func (s *Store) AddOAuthProvider(userID, provider string) error {
+	user, err := s.GetUser(userID)
+	if err != nil {
+		return fmt.Errorf("add oauth provider: %w", err)
+	}
+	if user == nil {
+		return fmt.Errorf("add oauth provider: user not found")
+	}
+
+	if user.HasOAuthProvider(provider) {
+		return nil // Already linked
+	}
+
+	providers := user.GetOAuthProviders()
+	providers = append(providers, provider)
+	data, err := json.Marshal(providers)
+	if err != nil {
+		return fmt.Errorf("add oauth provider: marshal: %w", err)
+	}
+
+	_, err = s.db.Exec(s.q(`UPDATE users SET oauth_providers = ?, updated_at = ? WHERE id = ?`),
+		string(data), now(), userID)
+	if err != nil {
+		return fmt.Errorf("add oauth provider: %w", err)
+	}
+	return nil
+}
+
+// RemoveOAuthProvider removes a provider from the user's oauth_providers list.
+func (s *Store) RemoveOAuthProvider(userID, provider string) error {
+	user, err := s.GetUser(userID)
+	if err != nil {
+		return fmt.Errorf("remove oauth provider: %w", err)
+	}
+	if user == nil {
+		return fmt.Errorf("remove oauth provider: user not found")
+	}
+
+	providers := user.GetOAuthProviders()
+	var filtered []string
+	for _, p := range providers {
+		if p != provider {
+			filtered = append(filtered, p)
+		}
+	}
+
+	var val string
+	if len(filtered) > 0 {
+		data, err := json.Marshal(filtered)
+		if err != nil {
+			return fmt.Errorf("remove oauth provider: marshal: %w", err)
+		}
+		val = string(data)
+	}
+
+	_, err = s.db.Exec(s.q(`UPDATE users SET oauth_providers = ?, updated_at = ? WHERE id = ?`),
+		val, now(), userID)
+	if err != nil {
+		return fmt.Errorf("remove oauth provider: %w", err)
+	}
+	return nil
+}
+
 // DeleteUser permanently deletes a user by ID.
 func (s *Store) DeleteUser(id string) error {
 	_, err := s.db.Exec(s.q(`DELETE FROM users WHERE id = ?`), id)
@@ -263,6 +406,55 @@ func (s *Store) DeleteUser(id string) error {
 	return nil
 }
 
+// DeleteAccountAtomic deletes a user and all their owned workspaces in a single
+// transaction. If any step fails, the entire operation is rolled back and no data
+// is modified. This prevents orphaned workspaces from partial deletions.
+func (s *Store) DeleteAccountAtomic(userID string, ownedWorkspaceSlugs []string) error {
+	tx, err := s.db.Begin()
+	if err != nil {
+		return fmt.Errorf("delete account: begin tx: %w", err)
+	}
+	defer tx.Rollback()
+
+	ts := now()
+
+	// 1. Soft-delete all owned workspaces
+	for _, slug := range ownedWorkspaceSlugs {
+		result, err := tx.Exec(s.q(`
+			UPDATE workspaces SET deleted_at = ?, updated_at = ?
+			WHERE slug = ? AND deleted_at IS NULL
+		`), ts, ts, slug)
+		if err != nil {
+			return fmt.Errorf("delete account: delete workspace %s: %w", slug, err)
+		}
+		rows, _ := result.RowsAffected()
+		if rows == 0 {
+			// Workspace already deleted or not found — not an error
+			continue
+		}
+	}
+
+	// 2. Revoke all sessions
+	if _, err := tx.Exec(s.q("DELETE FROM sessions WHERE user_id = ?"), userID); err != nil {
+		return fmt.Errorf("delete account: delete sessions: %w", err)
+	}
+
+	// 3. Revoke all API tokens
+	if _, err := tx.Exec(s.q("DELETE FROM api_tokens WHERE user_id = ?"), userID); err != nil {
+		return fmt.Errorf("delete account: delete api tokens: %w", err)
+	}
+
+	// 4. Delete the user record
+	if _, err := tx.Exec(s.q("DELETE FROM users WHERE id = ?"), userID); err != nil {
+		return fmt.Errorf("delete account: delete user: %w", err)
+	}
+
+	if err := tx.Commit(); err != nil {
+		return fmt.Errorf("delete account: commit: %w", err)
+	}
+	return nil
+}
+
 // --- Username backfill ---
 
 // GenerateUsername derives a URL-safe username from a display name.

web/src/lib/api/client.ts

@@ -51,6 +51,9 @@ class PadApiError extends Error {
 
 function getCSRFToken(): string | null {
 	if (typeof document === 'undefined') return null;
+	// Check __Host- prefixed cookie first (secure/TLS mode), fall back to unprefixed
+	const hostMatch = document.cookie.match(/(?:^|;\s*)__Host-pad_csrf=([^;]+)/);
+	if (hostMatch) return hostMatch[1];
 	const match = document.cookie.match(/(?:^|;\s*)pad_csrf=([^;]+)/);
 	return match ? match[1] : null;
 }
@@ -627,6 +630,11 @@ export const api = {
 				method: 'PATCH',
 				body: JSON.stringify(data)
 			}),
+		unlinkProvider: (provider: string) =>
+			request<{ ok: boolean; provider: string }>('/auth/oauth-unlink', {
+				method: 'POST',
+				body: JSON.stringify({ provider })
+			}),
 		tokens: {
 			list: () => request<APIToken[]>('/auth/tokens'),
 			create: (name: string) =>

web/src/lib/types/index.ts

@@ -7,6 +7,7 @@ export interface User {
 	name: string;
 	role: string;
 	avatar_url?: string;
+	oauth_providers?: string[];
 	created_at: string;
 	updated_at: string;
 }

web/src/routes/console/admin/+page.svelte

@@ -4,9 +4,12 @@
 
 	const BASE = '/api/v1';
 
-	function csrfToken(): string {
+	function getCSRFToken(): string | null {
+		// Check __Host- prefixed cookie first (secure/TLS mode), fall back to unprefixed
+		const hostMatch = document.cookie.match(/(?:^|;\s*)__Host-pad_csrf=([^;]+)/);
+		if (hostMatch) return hostMatch[1];
 		const match = document.cookie.match(/(?:^|;\s*)pad_csrf=([^;]+)/);
-		return match?.[1] ?? '';
+		return match ? match[1] : null;
 	}
 
 	async function adminFetch(path: string, opts?: RequestInit) {
@@ -16,9 +19,12 @@
 	}
 
 	async function adminPatch(path: string, body: unknown) {
+		const headers: Record<string, string> = { 'Content-Type': 'application/json' };
+		const csrf = getCSRFToken();
+		if (csrf) headers['X-CSRF-Token'] = csrf;
 		return adminFetch(path, {
 			method: 'PATCH',
-			headers: { 'Content-Type': 'application/json', 'X-CSRF-Token': csrfToken() },
+			headers,
 			body: JSON.stringify(body)
 		});
 	}

web/src/routes/console/billing/+page.svelte

@@ -3,12 +3,35 @@
 	import { goto } from '$app/navigation';
 	import { onMount } from 'svelte';
 
+	interface PlanLimits {
+		workspaces: number;
+		items_per_workspace: number;
+		members_per_workspace: number;
+		api_tokens: number;
+		storage_bytes: number;
+	}
+
 	let plan = $derived(authStore.user?.plan ?? 'free');
 	let isPro = $derived(plan === 'pro');
+	let limits = $state<{ free: PlanLimits; pro: PlanLimits } | null>(null);
 
-	onMount(() => {
+	function formatLimit(value: number | undefined): string {
+		if (value === undefined) return '...';
+		if (value === -1) return 'Unlimited';
+		return value.toLocaleString();
+	}
+
+	onMount(async () => {
 		if (!authStore.cloudMode) {
 			goto('/console', { replaceState: true });
+			return;
+		}
+
+		try {
+			const resp = await fetch('/api/v1/plan-limits', { credentials: 'same-origin' });
+			if (resp.ok) limits = await resp.json();
+		} catch {
+			/* use fallback rendering */
 		}
 	});
 </script>
@@ -58,11 +81,15 @@
 			</div>
 			<div class="usage-row">
 				<span class="usage-label">Workspaces</span>
-				<span class="usage-value">{isPro ? 'Unlimited' : 'Up to 5'}</span>
+				<span class="usage-value">{isPro ? formatLimit(limits?.pro?.workspaces) : formatLimit(limits?.free?.workspaces)}</span>
+			</div>
+			<div class="usage-row">
+				<span class="usage-label">Items per workspace</span>
+				<span class="usage-value">{isPro ? formatLimit(limits?.pro?.items_per_workspace) : formatLimit(limits?.free?.items_per_workspace)}</span>
 			</div>
 			<div class="usage-row">
 				<span class="usage-label">Members per workspace</span>
-				<span class="usage-value">{isPro ? 'Unlimited' : 'Up to 3'}</span>
+				<span class="usage-value">{isPro ? formatLimit(limits?.pro?.members_per_workspace) : formatLimit(limits?.free?.members_per_workspace)}</span>
 			</div>
 		</div>
 	</section>

web/src/routes/console/settings/+page.svelte

@@ -20,6 +20,23 @@
 	let passwordMsg = $state('');
 	let passwordError = $state('');
 
+	// OAuth providers
+	let providerMsg = $state('');
+	let providerError = $state('');
+
+	async function unlinkProvider(provider: string) {
+		providerMsg = '';
+		providerError = '';
+		try {
+			await api.auth.unlinkProvider(provider);
+			// Refresh profile to get updated providers list
+			profile = await api.auth.me();
+			providerMsg = `${provider === 'github' ? 'GitHub' : 'Google'} unlinked.`;
+		} catch (err) {
+			providerError = err instanceof Error ? err.message : 'Failed to unlink provider';
+		}
+	}
+
 	// Tokens
 	let tokens = $state<APIToken[]>([]);
 	let newTokenName = $state('');
@@ -201,6 +218,36 @@
 			</div>
 		</section>
 
+		<!-- Linked Accounts (cloud mode only) -->
+		{#if authStore.cloudMode}
+			<section class="card">
+				<h2 class="card-title">Linked Accounts</h2>
+				<div class="card-body">
+					<p class="section-desc">Link OAuth providers for single sign-on. You can sign in with any linked provider.</p>
+					{#each ['github', 'google'] as provider (provider)}
+						{@const linked = profile?.oauth_providers?.includes(provider) ?? false}
+						<div class="provider-row">
+							<div class="provider-info">
+								<span class="provider-name">{provider === 'github' ? 'GitHub' : 'Google'}</span>
+								{#if linked}
+									<span class="provider-badge linked">Linked</span>
+								{:else}
+									<span class="provider-badge">Not linked</span>
+								{/if}
+							</div>
+							{#if linked}
+								<button class="delete-btn" onclick={() => unlinkProvider(provider)}>Unlink</button>
+							{:else}
+								<a href="/auth/{provider}/link" class="primary-btn small">Link {provider === 'github' ? 'GitHub' : 'Google'}</a>
+							{/if}
+						</div>
+					{/each}
+					{#if providerMsg}<p class="success">{providerMsg}</p>{/if}
+					{#if providerError}<p class="error">{providerError}</p>{/if}
+				</div>
+			</section>
+		{/if}
+
 		<!-- API Tokens -->
 		<section class="card">
 			<h2 class="card-title">API Tokens</h2>
@@ -451,4 +498,51 @@
 		color: var(--text-muted);
 		font-size: 0.85rem;
 	}
+
+	.provider-row {
+		display: flex;
+		align-items: center;
+		justify-content: space-between;
+		padding: var(--space-3) var(--space-4);
+		background: var(--bg-tertiary);
+		border-radius: var(--radius);
+	}
+
+	.provider-info {
+		display: flex;
+		align-items: center;
+		gap: var(--space-3);
+	}
+
+	.provider-name {
+		font-weight: 500;
+		font-size: 0.9rem;
+		color: var(--text-primary);
+	}
+
+	.provider-badge {
+		padding: 2px var(--space-2);
+		border-radius: var(--radius-sm);
+		font-size: 0.75rem;
+		font-weight: 500;
+		background: color-mix(in srgb, var(--accent-gray, #888) 15%, transparent);
+		color: var(--text-muted);
+	}
+
+	.provider-badge.linked {
+		background: color-mix(in srgb, var(--accent-green) 15%, transparent);
+		color: var(--accent-green);
+	}
+
+	.section-desc {
+		font-size: 0.8rem;
+		color: var(--text-muted);
+		margin-top: calc(-1 * var(--space-2));
+	}
+
+	.primary-btn.small {
+		padding: var(--space-1) var(--space-3);
+		font-size: 0.8rem;
+		text-decoration: none;
+	}
 </style>