lib/api: Save session & CSRF tokens to database, add option to stay logged in (fixes #9151) (#9284)

This adds a "token manager" which handles storing and checking expired
tokens, used for both sessions and CSRF tokens. It removes the old,
corresponding functionality for CSRFs which saved things in a file. The
result is less crap in the state directory, and active login sessions
now survive a Syncthing restart (this really annoyed me).

It also adds a boolean on login to create a longer-lived session cookie,
which is now possible and useful. Thus we can remain logged in over
browser restarts, which was also annoying... :)

<img width="1001" alt="Screenshot 2023-12-12 at 09 56 34"
src="https://github.com/syncthing/syncthing/assets/125426/55cb20c8-78fc-453e-825d-655b94c8623b">

Best viewed with whitespace-insensitive diff, as a bunch of the auth
functions became methods instead of closures which changed indentation.

14 files changed, 785 insertions, 272 deletions

diff --git a/cmd/syncthing/main.go b/cmd/syncthing/main.go
index f321ebc8b..ab3c76e73 100644
--- a/cmd/syncthing/main.go
+++ b/cmd/syncthing/main.go
@@ -862,6 +862,7 @@ func cleanConfigDirectory() {
 		"backup-of-v0.8":     30 * 24 * time.Hour, // these neither
 		"tmp-index-sorter.*": time.Minute,         // these should never exist on startup
 		"support-bundle-*":   30 * 24 * time.Hour, // keep old support bundle zip or folder for a month
+		"csrftokens.txt":     0,                   // deprecated, remove immediately
 	}
 
 	for pat, dur := range patterns {
diff --git a/gui/default/index.html b/gui/default/index.html
index 6e26461ce..7f5baa99e 100644
--- a/gui/default/index.html
+++ b/gui/default/index.html
@@ -359,6 +359,12 @@
             <input id="password" class="form-control" type="password" name="password" ng-model="login.password" ng-trim="false" autocomplete="current-password" />
           </div>
 
+          <div class="form-group">
+            <label>
+              <input type="checkbox" ng-model="login.stayLoggedIn" >&nbsp;<span translate>Stay logged in</span>
+            </label>
+          </div>
+
           <div class="row">
             <div class="col-md-9 login-form-messages">
               <p ng-if="login.errors.badLogin" class="text-danger" translate>
diff --git a/gui/default/syncthing/core/syncthingController.js b/gui/default/syncthing/core/syncthingController.js
index b31f94188..54b0a96ee 100755
--- a/gui/default/syncthing/core/syncthingController.js
+++ b/gui/default/syncthing/core/syncthingController.js
@@ -103,6 +103,7 @@ angular.module('syncthing.core')
             $http.post(authUrlbase + '/password', {
               username: $scope.login.username,
               password: $scope.login.password,
+              stayLoggedIn: $scope.login.stayLoggedIn,
             }).then(function () {
                 location.reload();
             }).catch(function (response) {
@@ -3602,7 +3603,7 @@ angular.module('syncthing.core')
                 return n.match !== "";
             });
         };
-        
+
         // The showModal and hideModal functions are a bandaid for a Bootstrap
         // bug (see https://github.com/twbs/bootstrap/issues/3902) that causes
         // multiple consecutively shown or hidden modals to overlap which leads
diff --git a/lib/api/api.go b/lib/api/api.go
index c316310c8..b96fc14ee 100644
--- a/lib/api/api.go
+++ b/lib/api/api.go
@@ -91,6 +91,7 @@ type service struct {
 	startupErr           error
 	listenerAddr         net.Addr
 	exitChan             chan *svcutil.FatalErr
+	miscDB               *db.NamespacedKV
 
 	guiErrors logger.Recorder
 	systemLog logger.Recorder
@@ -104,7 +105,7 @@ type Service interface {
 	WaitForStart() error
 }
 
-func New(id protocol.DeviceID, cfg config.Wrapper, assetDir, tlsDefaultCommonName string, m model.Model, defaultSub, diskSub events.BufferedSubscription, evLogger events.Logger, discoverer discover.Manager, connectionsService connections.Service, urService *ur.Service, fss model.FolderSummaryService, errors, systemLog logger.Recorder, noUpgrade bool) Service {
+func New(id protocol.DeviceID, cfg config.Wrapper, assetDir, tlsDefaultCommonName string, m model.Model, defaultSub, diskSub events.BufferedSubscription, evLogger events.Logger, discoverer discover.Manager, connectionsService connections.Service, urService *ur.Service, fss model.FolderSummaryService, errors, systemLog logger.Recorder, noUpgrade bool, miscDB *db.NamespacedKV) Service {
 	return &service{
 		id:      id,
 		cfg:     cfg,
@@ -127,6 +128,7 @@ func New(id protocol.DeviceID, cfg config.Wrapper, assetDir, tlsDefaultCommonNam
 		configChanged:        make(chan struct{}),
 		startedOnce:          make(chan struct{}),
 		exitChan:             make(chan *svcutil.FatalErr, 1),
+		miscDB:               miscDB,
 	}
 }
 
@@ -364,7 +366,7 @@ func (s *service) Serve(ctx context.Context) error {
 
 	// Wrap everything in CSRF protection. The /rest prefix should be
 	// protected, other requests will grant cookies.
-	var handler http.Handler = newCsrfManager(s.id.Short().String(), "/rest", guiCfg, mux, locations.Get(locations.CsrfTokens))
+	var handler http.Handler = newCsrfManager(s.id.Short().String(), "/rest", guiCfg, mux, s.miscDB)
 
 	// Add our version and ID as a header to responses
 	handler = withDetailsMiddleware(s.id, handler)
@@ -372,12 +374,13 @@ func (s *service) Serve(ctx context.Context) error {
 	// Wrap everything in basic auth, if user/password is set.
 	if guiCfg.IsAuthEnabled() {
 		sessionCookieName := "sessionid-" + s.id.Short().String()
-		handler = basicAuthAndSessionMiddleware(sessionCookieName, s.id.Short().String(), guiCfg, s.cfg.LDAP(), handler, s.evLogger)
-		handlePasswordAuth := passwordAuthHandler(sessionCookieName, guiCfg, s.cfg.LDAP(), s.evLogger)
-		restMux.Handler(http.MethodPost, "/rest/noauth/auth/password", handlePasswordAuth)
+		authMW := newBasicAuthAndSessionMiddleware(sessionCookieName, s.id.Short().String(), guiCfg, s.cfg.LDAP(), handler, s.evLogger, s.miscDB)
+		handler = authMW
+
+		restMux.Handler(http.MethodPost, "/rest/noauth/auth/password", http.HandlerFunc(authMW.passwordAuthHandler))
 
 		// Logout is a no-op without a valid session cookie, so /noauth/ is fine here
-		restMux.Handler(http.MethodPost, "/rest/noauth/auth/logout", handleLogout(sessionCookieName))
+		restMux.Handler(http.MethodPost, "/rest/noauth/auth/logout", http.HandlerFunc(authMW.handleLogout))
 	}
 
 	// Redirect to HTTPS if we are supposed to
diff --git a/lib/api/api_auth.go b/lib/api/api_auth.go
index 7af4faacb..cee0397ad 100644
--- a/lib/api/api_auth.go
+++ b/lib/api/api_auth.go
@@ -16,15 +16,16 @@ import (
 
 	ldap "github.com/go-ldap/ldap/v3"
 	"github.com/syncthing/syncthing/lib/config"
+	"github.com/syncthing/syncthing/lib/db"
 	"github.com/syncthing/syncthing/lib/events"
 	"github.com/syncthing/syncthing/lib/rand"
-	"github.com/syncthing/syncthing/lib/sync"
 	"golang.org/x/exp/slices"
 )
 
-var (
-	sessions    = make(map[string]bool)
-	sessionsMut = sync.NewMutex()
+const (
+	maxSessionLifetime = 7 * 24 * time.Hour
+	maxActiveSessions  = 25
+	randomTokenLength  = 64
 )
 
 func emitLoginAttempt(success bool, username, address string, evLogger events.Logger) {
@@ -78,75 +79,91 @@ func isNoAuthPath(path string) bool {
 		})
 }
 
-func basicAuthAndSessionMiddleware(cookieName, shortID string, guiCfg config.GUIConfiguration, ldapCfg config.LDAPConfiguration, next http.Handler, evLogger events.Logger) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		if hasValidAPIKeyHeader(r, guiCfg) {
-			next.ServeHTTP(w, r)
-			return
-		}
+type basicAuthAndSessionMiddleware struct {
+	cookieName string
+	shortID    string
+	guiCfg     config.GUIConfiguration
+	ldapCfg    config.LDAPConfiguration
+	next       http.Handler
+	evLogger   events.Logger
+	tokens     *tokenManager
+}
+
+func newBasicAuthAndSessionMiddleware(cookieName, shortID string, guiCfg config.GUIConfiguration, ldapCfg config.LDAPConfiguration, next http.Handler, evLogger events.Logger, miscDB *db.NamespacedKV) *basicAuthAndSessionMiddleware {
+	return &basicAuthAndSessionMiddleware{
+		cookieName: cookieName,
+		shortID:    shortID,
+		guiCfg:     guiCfg,
+		ldapCfg:    ldapCfg,
+		next:       next,
+		evLogger:   evLogger,
+		tokens:     newTokenManager("sessions", miscDB, maxSessionLifetime, maxActiveSessions),
+	}
+}
+
+func (m *basicAuthAndSessionMiddleware) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if hasValidAPIKeyHeader(r, m.guiCfg) {
+		m.next.ServeHTTP(w, r)
+		return
+	}
 
-		for _, cookie := range r.Cookies() {
-			// We iterate here since there may, historically, be multiple
-			// cookies with the same name but different path. Any "old" ones
-			// won't match an existing session and will be ignored, then
-			// later removed on logout or when timing out.
-			if cookie.Name == cookieName {
-				sessionsMut.Lock()
-				_, ok := sessions[cookie.Value]
-				sessionsMut.Unlock()
-				if ok {
-					next.ServeHTTP(w, r)
-					return
-				}
+	for _, cookie := range r.Cookies() {
+		// We iterate here since there may, historically, be multiple
+		// cookies with the same name but different path. Any "old" ones
+		// won't match an existing session and will be ignored, then
+		// later removed on logout or when timing out.
+		if cookie.Name == m.cookieName {
+			if m.tokens.Check(cookie.Value) {
+				m.next.ServeHTTP(w, r)
+				return
 			}
 		}
+	}
 
-		// Fall back to Basic auth if provided
-		if username, ok := attemptBasicAuth(r, guiCfg, ldapCfg, evLogger); ok {
-			createSession(cookieName, username, guiCfg, evLogger, w, r)
-			next.ServeHTTP(w, r)
-			return
-		}
+	// Fall back to Basic auth if provided
+	if username, ok := attemptBasicAuth(r, m.guiCfg, m.ldapCfg, m.evLogger); ok {
+		m.createSession(username, false, w, r)
+		m.next.ServeHTTP(w, r)
+		return
+	}
 
-		// Exception for static assets and REST calls that don't require authentication.
-		if isNoAuthPath(r.URL.Path) {
-			next.ServeHTTP(w, r)
-			return
-		}
+	// Exception for static assets and REST calls that don't require authentication.
+	if isNoAuthPath(r.URL.Path) {
+		m.next.ServeHTTP(w, r)
+		return
+	}
 
-		// Some browsers don't send the Authorization request header unless prompted by a 401 response.
-		// This enables https://user:pass@localhost style URLs to keep working.
-		if guiCfg.SendBasicAuthPrompt {
-			unauthorized(w, shortID)
-			return
-		}
+	// Some browsers don't send the Authorization request header unless prompted by a 401 response.
+	// This enables https://user:pass@localhost style URLs to keep working.
+	if m.guiCfg.SendBasicAuthPrompt {
+		unauthorized(w, m.shortID)
+		return
+	}
 
-		forbidden(w)
-	})
+	forbidden(w)
 }
 
-func passwordAuthHandler(cookieName string, guiCfg config.GUIConfiguration, ldapCfg config.LDAPConfiguration, evLogger events.Logger) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		var req struct {
-			Username string
-			Password string
-		}
-		if err := unmarshalTo(r.Body, &req); err != nil {
-			l.Debugln("Failed to parse username and password:", err)
-			http.Error(w, "Failed to parse username and password.", http.StatusBadRequest)
-			return
-		}
+func (m *basicAuthAndSessionMiddleware) passwordAuthHandler(w http.ResponseWriter, r *http.Request) {
+	var req struct {
+		Username     string
+		Password     string
+		StayLoggedIn bool
+	}
+	if err := unmarshalTo(r.Body, &req); err != nil {
+		l.Debugln("Failed to parse username and password:", err)
+		http.Error(w, "Failed to parse username and password.", http.StatusBadRequest)
+		return
+	}
 
-		if auth(req.Username, req.Password, guiCfg, ldapCfg) {
-			createSession(cookieName, req.Username, guiCfg, evLogger, w, r)
-			w.WriteHeader(http.StatusNoContent)
-			return
-		}
+	if auth(req.Username, req.Password, m.guiCfg, m.ldapCfg) {
+		m.createSession(req.Username, req.StayLoggedIn, w, r)
+		w.WriteHeader(http.StatusNoContent)
+		return
+	}
 
-		emitLoginAttempt(false, req.Username, r.RemoteAddr, evLogger)
-		antiBruteForceSleep()
-		forbidden(w)
-	})
+	emitLoginAttempt(false, req.Username, r.RemoteAddr, m.evLogger)
+	antiBruteForceSleep()
+	forbidden(w)
 }
 
 func attemptBasicAuth(r *http.Request, guiCfg config.GUIConfiguration, ldapCfg config.LDAPConfiguration, evLogger events.Logger) (string, bool) {
@@ -172,11 +189,8 @@ func attemptBasicAuth(r *http.Request, guiCfg config.GUIConfiguration, ldapCfg c
 	return "", false
 }
 
-func createSession(cookieName string, username string, guiCfg config.GUIConfiguration, evLogger events.Logger, w http.ResponseWriter, r *http.Request) {
-	sessionid := rand.String(32)
-	sessionsMut.Lock()
-	sessions[sessionid] = true
-	sessionsMut.Unlock()
+func (m *basicAuthAndSessionMiddleware) createSession(username string, persistent bool, w http.ResponseWriter, r *http.Request) {
+	sessionid := m.tokens.New()
 
 	// Best effort detection of whether the connection is HTTPS --
 	// either directly to us, or as used by the client towards a reverse
@@ -186,45 +200,45 @@ func createSession(cookieName string, username string, guiCfg config.GUIConfigur
 		strings.Contains(strings.ToLower(r.Header.Get("forwarded")), "proto=https")
 	// If the connection is HTTPS, or *should* be HTTPS, set the Secure
 	// bit in cookies.
-	useSecureCookie := connectionIsHTTPS || guiCfg.UseTLS()
+	useSecureCookie := connectionIsHTTPS || m.guiCfg.UseTLS()
 
+	maxAge := 0
+	if persistent {
+		maxAge = int(maxSessionLifetime.Seconds())
+	}
 	http.SetCookie(w, &http.Cookie{
-		Name:  cookieName,
+		Name:  m.cookieName,
 		Value: sessionid,
 		// In HTTP spec Max-Age <= 0 means delete immediately,
 		// but in http.Cookie MaxAge = 0 means unspecified (session) and MaxAge < 0 means delete immediately
-		MaxAge: 0,
+		MaxAge: maxAge,
 		Secure: useSecureCookie,
 		Path:   "/",
 	})
 
-	emitLoginAttempt(true, username, r.RemoteAddr, evLogger)
+	emitLoginAttempt(true, username, r.RemoteAddr, m.evLogger)
 }
 
-func handleLogout(cookieName string) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		for _, cookie := range r.Cookies() {
-			// We iterate here since there may, historically, be multiple
-			// cookies with the same name but different path. We drop them
-			// all.
-			if cookie.Name == cookieName {
-				sessionsMut.Lock()
-				delete(sessions, cookie.Value)
-				sessionsMut.Unlock()
-
-				// Delete the cookie
-				http.SetCookie(w, &http.Cookie{
-					Name:   cookieName,
-					Value:  "",
-					MaxAge: -1,
-					Secure: cookie.Secure,
-					Path:   cookie.Path,
-				})
-			}
+func (m *basicAuthAndSessionMiddleware) handleLogout(w http.ResponseWriter, r *http.Request) {
+	for _, cookie := range r.Cookies() {
+		// We iterate here since there may, historically, be multiple
+		// cookies with the same name but different path. We drop them
+		// all.
+		if cookie.Name == m.cookieName {
+			m.tokens.Delete(cookie.Value)
+
+			// Delete the cookie
+			http.SetCookie(w, &http.Cookie{
+				Name:   m.cookieName,
+				Value:  "",
+				MaxAge: -1,
+				Secure: cookie.Secure,
+				Path:   cookie.Path,
+			})
 		}
+	}
 
-		w.WriteHeader(http.StatusNoContent)
-	})
+	w.WriteHeader(http.StatusNoContent)
 }
 
 func auth(username string, password string, guiCfg config.GUIConfiguration, ldapCfg config.LDAPConfiguration) bool {
diff --git a/lib/api/api_auth_test.go b/lib/api/api_auth_test.go
index e4e207a09..a2d7146d9 100644
--- a/lib/api/api_auth_test.go
+++ b/lib/api/api_auth_test.go
@@ -8,8 +8,12 @@ package api
 
 import (
 	"testing"
+	"time"
 
 	"github.com/syncthing/syncthing/lib/config"
+	"github.com/syncthing/syncthing/lib/db"
+	"github.com/syncthing/syncthing/lib/db/backend"
+	"github.com/syncthing/syncthing/lib/events"
 )
 
 var guiCfg config.GUIConfiguration
@@ -110,3 +114,76 @@ func TestEscapeForLDAPDN(t *testing.T) {
 		}
 	}
 }
+
+type mockClock struct {
+	now time.Time
+}
+
+func (c *mockClock) Now() time.Time {
+	c.now = c.now.Add(1) // time always ticks by at least 1 ns
+	return c.now
+}
+
+func (c *mockClock) wind(t time.Duration) {
+	c.now = c.now.Add(t)
+}
+
+func TestTokenManager(t *testing.T) {
+	t.Parallel()
+
+	mdb, _ := db.NewLowlevel(backend.OpenMemory(), events.NoopLogger)
+	kdb := db.NewNamespacedKV(mdb, "test")
+	clock := &mockClock{now: time.Now()}
+
+	// Token manager keeps up to three tokens with a validity time of 24 hours.
+	tm := newTokenManager("testTokens", kdb, 24*time.Hour, 3)
+	tm.timeNow = clock.Now
+
+	// Create three tokens
+	t0 := tm.New()
+	t1 := tm.New()
+	t2 := tm.New()
+
+	// Check that the tokens are valid
+	if !tm.Check(t0) {
+		t.Errorf("token %q should be valid", t0)
+	}
+	if !tm.Check(t1) {
+		t.Errorf("token %q should be valid", t1)
+	}
+	if !tm.Check(t2) {
+		t.Errorf("token %q should be valid", t2)
+	}
+
+	// Create a fourth token
+	t3 := tm.New()
+	// It should be valid
+	if !tm.Check(t3) {
+		t.Errorf("token %q should be valid", t3)
+	}
+	// But the first token should have been removed
+	if tm.Check(t0) {
+		t.Errorf("token %q should be invalid", t0)
+	}
+
+	// Wind the clock by 12 hours
+	clock.wind(12 * time.Hour)
+	// The second token should still be valid (and checking it will give it more life)
+	if !tm.Check(t1) {
+		t.Errorf("token %q should be valid", t1)
+	}
+
+	// Wind the clock by 12 hours
+	clock.wind(12 * time.Hour)
+	// The second token should still be valid
+	if !tm.Check(t1) {
+		t.Errorf("token %q should be valid", t1)
+	}
+	// But the third and fourth tokens should have expired
+	if tm.Check(t2) {
+		t.Errorf("token %q should be invalid", t2)
+	}
+	if tm.Check(t3) {
+		t.Errorf("token %q should be invalid", t3)
+	}
+}
diff --git a/lib/api/api_csrf.go b/lib/api/api_csrf.go
index 2a309a4e8..e8f03418d 100644
--- a/lib/api/api_csrf.go
+++ b/lib/api/api_csrf.go
@@ -7,33 +7,24 @@
 package api
 
 import (
-	"bufio"
-	"fmt"
 	"net/http"
-	"os"
 	"strings"
+	"time"
 
-	"github.com/syncthing/syncthing/lib/osutil"
-	"github.com/syncthing/syncthing/lib/rand"
-	"github.com/syncthing/syncthing/lib/sync"
+	"github.com/syncthing/syncthing/lib/db"
 )
 
-const maxCsrfTokens = 25
+const (
+	maxCSRFTokenLifetime = time.Hour
+	maxActiveCSRFTokens  = 25
+)
 
 type csrfManager struct {
-	// tokens is a list of valid tokens. It is sorted so that the most
-	// recently used token is first in the list. New tokens are added to the front
-	// of the list (as it is the most recently used at that time). The list is
-	// pruned to a maximum of maxCsrfTokens, throwing away the least recently used
-	// tokens.
-	tokens    []string
-	tokensMut sync.Mutex
-
 	unique          string
 	prefix          string
 	apiKeyValidator apiKeyValidator
 	next            http.Handler
-	saveLocation    string
+	tokens          *tokenManager
 }
 
 type apiKeyValidator interface {
@@ -43,17 +34,14 @@ type apiKeyValidator interface {
 // Check for CSRF token on /rest/ URLs. If a correct one is not given, reject
 // the request with 403. For / and /index.html, set a new CSRF cookie if none
 // is currently set.
-func newCsrfManager(unique string, prefix string, apiKeyValidator apiKeyValidator, next http.Handler, saveLocation string) *csrfManager {
+func newCsrfManager(unique string, prefix string, apiKeyValidator apiKeyValidator, next http.Handler, miscDB *db.NamespacedKV) *csrfManager {
 	m := &csrfManager{
-		tokensMut:       sync.NewMutex(),
-		tokens:          make([]string, 0, maxCsrfTokens),
 		unique:          unique,
 		prefix:          prefix,
 		apiKeyValidator: apiKeyValidator,
 		next:            next,
-		saveLocation:    saveLocation,
+		tokens:          newTokenManager("csrfTokens", miscDB, maxCSRFTokenLifetime, maxActiveCSRFTokens),
 	}
-	m.load()
 	return m
 }
 
@@ -78,11 +66,11 @@ func (m *csrfManager) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	// and set a CSRF cookie if there isn't already a valid one.
 	if !strings.HasPrefix(r.URL.Path, m.prefix) {
 		cookie, err := r.Cookie("CSRF-Token-" + m.unique)
-		if err != nil || !m.validToken(cookie.Value) {
+		if err != nil || !m.tokens.Check(cookie.Value) {
 			l.Debugln("new CSRF cookie in response to request for", r.URL)
 			cookie = &http.Cookie{
 				Name:  "CSRF-Token-" + m.unique,
-				Value: m.newToken(),
+				Value: m.tokens.New(),
 			}
 			http.SetCookie(w, cookie)
 		}
@@ -99,7 +87,7 @@ func (m *csrfManager) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	// Verify the CSRF token
 	token := r.Header.Get("X-CSRF-Token-" + m.unique)
-	if !m.validToken(token) {
+	if !m.tokens.Check(token) {
 		http.Error(w, "CSRF Error", http.StatusForbidden)
 		return
 	}
@@ -107,78 +95,6 @@ func (m *csrfManager) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	m.next.ServeHTTP(w, r)
 }
 
-func (m *csrfManager) validToken(token string) bool {
-	m.tokensMut.Lock()
-	defer m.tokensMut.Unlock()
-	for i, t := range m.tokens {
-		if t == token {
-			if i > 0 {
-				// Move this token to the head of the list. Copy the tokens at
-				// the front one step to the right and then replace the token
-				// at the head.
-				copy(m.tokens[1:], m.tokens[:i])
-				m.tokens[0] = token
-			}
-			return true
-		}
-	}
-	return false
-}
-
-func (m *csrfManager) newToken() string {
-	token := rand.String(32)
-
-	m.tokensMut.Lock()
-	defer m.tokensMut.Unlock()
-
-	if len(m.tokens) < maxCsrfTokens {
-		m.tokens = append(m.tokens, "")
-	}
-	copy(m.tokens[1:], m.tokens)
-	m.tokens[0] = token
-
-	m.save()
-
-	return token
-}
-
-func (m *csrfManager) save() {
-	// We're ignoring errors in here. It's not super critical and there's
-	// nothing relevant we can do about them anyway...
-
-	if m.saveLocation == "" {
-		return
-	}
-
-	f, err := osutil.CreateAtomic(m.saveLocation)
-	if err != nil {
-		return
-	}
-
-	for _, t := range m.tokens {
-		fmt.Fprintln(f, t)
-	}
-
-	f.Close()
-}
-
-func (m *csrfManager) load() {
-	if m.saveLocation == "" {
-		return
-	}
-
-	f, err := os.Open(m.saveLocation)
-	if err != nil {
-		return
-	}
-	defer f.Close()
-
-	s := bufio.NewScanner(f)
-	for s.Scan() {
-		m.tokens = append(m.tokens, s.Text())
-	}
-}
-
 func hasValidAPIKeyHeader(r *http.Request, validator apiKeyValidator) bool {
 	if key := r.Header.Get("X-API-Key"); validator.IsValidAPIKey(key) {
 		return true
diff --git a/lib/api/api_test.go b/lib/api/api_test.go
index 72c2ff381..facbb85e6 100644
--- a/lib/api/api_test.go
+++ b/lib/api/api_test.go
@@ -18,7 +18,6 @@ import (
 	"net/http/httptest"
 	"os"
 	"path/filepath"
-	"reflect"
 	"strconv"
 	"strings"
 	"testing"
@@ -29,6 +28,8 @@ import (
 	"github.com/syncthing/syncthing/lib/build"
 	"github.com/syncthing/syncthing/lib/config"
 	connmocks "github.com/syncthing/syncthing/lib/connections/mocks"
+	"github.com/syncthing/syncthing/lib/db"
+	"github.com/syncthing/syncthing/lib/db/backend"
 	discovermocks "github.com/syncthing/syncthing/lib/discover/mocks"
 	"github.com/syncthing/syncthing/lib/events"
 	eventmocks "github.com/syncthing/syncthing/lib/events/mocks"
@@ -72,71 +73,6 @@ func TestMain(m *testing.M) {
 	os.Exit(exitCode)
 }
 
-func TestCSRFToken(t *testing.T) {
-	t.Parallel()
-
-	max := 10 * maxCsrfTokens
-	int := 5
-	if testing.Short() {
-		max = 1 + maxCsrfTokens
-		int = 2
-	}
-
-	m := newCsrfManager("unique", "prefix", config.GUIConfiguration{}, nil, "")
-
-	t1 := m.newToken()
-	t2 := m.newToken()
-
-	t3 := m.newToken()
-	if !m.validToken(t3) {
-		t.Fatal("t3 should be valid")
-	}
-
-	valid := make(map[string]struct{}, maxCsrfTokens)
-	for _, token := range m.tokens {
-		valid[token] = struct{}{}
-	}
-
-	for i := 0; i < max; i++ {
-		if i%int == 0 {
-			// t1 and t2 should remain valid by virtue of us checking them now
-			// and then.
-			if !m.validToken(t1) {
-				t.Fatal("t1 should be valid at iteration", i)
-			}
-			if !m.validToken(t2) {
-				t.Fatal("t2 should be valid at iteration", i)
-			}
-		}
-
-		if len(m.tokens) == maxCsrfTokens {
-			// We're about to add a token, which will remove the last token
-			// from m.tokens.
-			delete(valid, m.tokens[len(m.tokens)-1])
-		}
-
-		// The newly generated token is always valid
-		t4 := m.newToken()
-		if !m.validToken(t4) {
-			t.Fatal("t4 should be valid at iteration", i)
-		}
-		valid[t4] = struct{}{}
-
-		v := make(map[string]struct{}, maxCsrfTokens)
-		for _, token := range m.tokens {
-			v[token] = struct{}{}
-		}
-
-		if !reflect.DeepEqual(v, valid) {
-			t.Fatalf("want valid tokens %v, got %v", valid, v)
-		}
-	}
-
-	if m.validToken(t3) {
-		t.Fatal("t3 should have expired by now")
-	}
-}
-
 func TestStopAfterBrokenConfig(t *testing.T) {
 	t.Parallel()
 
@@ -148,7 +84,9 @@ func TestStopAfterBrokenConfig(t *testing.T) {
 	}
 	w := config.Wrap("/dev/null", cfg, protocol.LocalDeviceID, events.NoopLogger)
 
-	srv := New(protocol.LocalDeviceID, w, "", "syncthing", nil, nil, nil, events.NoopLogger, nil, nil, nil, nil, nil, nil, false).(*service)
+	mdb, _ := db.NewLowlevel(backend.OpenMemory(), events.NoopLogger)
+	kdb := db.NewMiscDataNamespace(mdb)
+	srv := New(protocol.LocalDeviceID, w, "", "syncthing", nil, nil, nil, events.NoopLogger, nil, nil, nil, nil, nil, nil, false, kdb).(*service)
 	defer os.Remove(token)
 
 	srv.started = make(chan string)
@@ -926,7 +864,9 @@ func startHTTP(cfg config.Wrapper) (string, context.CancelFunc, error) {
 
 	// Instantiate the API service
 	urService := ur.New(cfg, m, connections, false)
-	svc := New(protocol.LocalDeviceID, cfg, assetDir, "syncthing", m, eventSub, diskEventSub, events.NoopLogger, discoverer, connections, urService, mockedSummary, errorLog, systemLog, false).(*service)
+	mdb, _ := db.NewLowlevel(backend.OpenMemory(), events.NoopLogger)
+	kdb := db.NewMiscDataNamespace(mdb)
+	svc := New(protocol.LocalDeviceID, cfg, assetDir, "syncthing", m, eventSub, diskEventSub, events.NoopLogger, discoverer, connections, urService, mockedSummary, errorLog, systemLog, false, kdb).(*service)
 	defer os.Remove(token)
 	svc.started = addrChan
 
@@ -1467,7 +1407,9 @@ func TestEventMasks(t *testing.T) {
 	cfg := newMockedConfig()
 	defSub := new(eventmocks.BufferedSubscription)
 	diskSub := new(eventmocks.BufferedSubscription)
-	svc := New(protocol.LocalDeviceID, cfg, "", "syncthing", nil, defSub, diskSub, events.NoopLogger, nil, nil, nil, nil, nil, nil, false).(*service)
+	mdb, _ := db.NewLowlevel(backend.OpenMemory(), events.NoopLogger)
+	kdb := db.NewMiscDataNamespace(mdb)
+	svc := New(protocol.LocalDeviceID, cfg, "", "syncthing", nil, defSub, diskSub, events.NoopLogger, nil, nil, nil, nil, nil, nil, false, kdb).(*service)
 	defer os.Remove(token)
 
 	if mask := svc.getEventMask(""); mask != DefaultEventMask {
diff --git a/lib/api/tokenmanager.go b/lib/api/tokenmanager.go
new file mode 100644
index 000000000..d03c75923
--- /dev/null
+++ b/lib/api/tokenmanager.go
@@ -0,0 +1,137 @@
+// Copyright (C) 2024 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package api
+
+import (
+	"time"
+
+	"github.com/syncthing/syncthing/lib/db"
+	"github.com/syncthing/syncthing/lib/rand"
+	"github.com/syncthing/syncthing/lib/sync"
+	"golang.org/x/exp/slices"
+)
+
+type tokenManager struct {
+	key      string
+	miscDB   *db.NamespacedKV
+	lifetime time.Duration
+	maxItems int
+
+	timeNow func() time.Time // can be overridden for testing
+
+	mut       sync.Mutex
+	tokens    *TokenSet
+	saveTimer *time.Timer
+}
+
+func newTokenManager(key string, miscDB *db.NamespacedKV, lifetime time.Duration, maxItems int) *tokenManager {
+	tokens := &TokenSet{
+		Tokens: make(map[string]int64),
+	}
+	if bs, ok, _ := miscDB.Bytes(key); ok {
+		_ = tokens.Unmarshal(bs) // best effort
+	}
+	return &tokenManager{
+		key:      key,
+		miscDB:   miscDB,
+		lifetime: lifetime,
+		maxItems: maxItems,
+		timeNow:  time.Now,
+		mut:      sync.NewMutex(),
+		tokens:   tokens,
+	}
+}
+
+// Check returns true if the token is valid, and updates the token's expiry
+// time. The token is removed if it is expired.
+func (m *tokenManager) Check(token string) bool {
+	m.mut.Lock()
+	defer m.mut.Unlock()
+
+	expires, ok := m.tokens.Tokens[token]
+	if ok {
+		if expires < m.timeNow().UnixNano() {
+			// The token is expired.
+			m.saveLocked() // removes expired tokens
+			return false
+		}
+
+		// Give the token further life.
+		m.tokens.Tokens[token] = m.timeNow().Add(m.lifetime).UnixNano()
+		m.saveLocked()
+	}
+	return ok
+}
+
+// New creates a new token and returns it.
+func (m *tokenManager) New() string {
+	token := rand.String(randomTokenLength)
+
+	m.mut.Lock()
+	defer m.mut.Unlock()
+
+	m.tokens.Tokens[token] = m.timeNow().Add(m.lifetime).UnixNano()
+	m.saveLocked()
+
+	return token
+}
+
+// Delete removes a token.
+func (m *tokenManager) Delete(token string) {
+	m.mut.Lock()
+	defer m.mut.Unlock()
+
+	delete(m.tokens.Tokens, token)
+	m.saveLocked()
+}
+
+func (m *tokenManager) saveLocked() {
+	// Remove expired tokens.
+	now := m.timeNow().UnixNano()
+	for token, expiry := range m.tokens.Tokens {
+		if expiry < now {
+			delete(m.tokens.Tokens, token)
+		}
+	}
+
+	// If we have a limit on the number of tokens, remove the oldest ones.
+	if m.maxItems > 0 && len(m.tokens.Tokens) > m.maxItems {
+		// Sort the tokens by expiry time, oldest first.
+		type tokenExpiry struct {
+			token  string
+			expiry int64
+		}
+		var tokens []tokenExpiry
+		for token, expiry := range m.tokens.Tokens {
+			tokens = append(tokens, tokenExpiry{token, expiry})
+		}
+		slices.SortFunc(tokens, func(i, j tokenExpiry) int {
+			return int(i.expiry - j.expiry)
+		})
+		// Remove the oldest tokens.
+		for _, token := range tokens[:len(tokens)-m.maxItems] {
+			delete(m.tokens.Tokens, token.token)
+		}
+	}
+
+	// Postpone saving until one second of inactivity.
+	if m.saveTimer == nil {
+		m.saveTimer = time.AfterFunc(time.Second, m.scheduledSave)
+	} else {
+		m.saveTimer.Reset(time.Second)
+	}
+}
+
+func (m *tokenManager) scheduledSave() {
+	m.mut.Lock()
+	defer m.mut.Unlock()
+
+	m.saveTimer = nil
+
+	bs, _ := m.tokens.Marshal()      // can't fail
+	_ = m.miscDB.PutBytes(m.key, bs) // can fail, but what are we going to do?
+}
diff --git a/lib/api/tokenset.pb.go b/lib/api/tokenset.pb.go
new file mode 100644
index 000000000..80883fab2
--- /dev/null
+++ b/lib/api/tokenset.pb.go
@@ -0,0 +1,411 @@
+// Code generated by protoc-gen-gogo. DO NOT EDIT.
+// source: lib/api/tokenset.proto
+
+package api
+
+import (
+	fmt "fmt"
+	proto "github.com/gogo/protobuf/proto"
+	io "io"
+	math "math"
+	math_bits "math/bits"
+)
+
+// Reference imports to suppress errors if they are not otherwise used.
+var _ = proto.Marshal
+var _ = fmt.Errorf
+var _ = math.Inf
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the proto package it is being compiled against.
+// A compilation error at this line likely means your copy of the
+// proto package needs to be updated.
+const _ = proto.GoGoProtoPackageIsVersion3 // please upgrade the proto package
+
+type TokenSet struct {
+	// token -> expiry time (epoch nanoseconds)
+	Tokens map[string]int64 `protobuf:"bytes,1,rep,name=tokens,proto3" json:"tokens" xml:"token" protobuf_key:"bytes,1,opt,name=key,proto3" protobuf_val:"varint,2,opt,name=value,proto3"`
+}
+
+func (m *TokenSet) Reset()         { *m = TokenSet{} }
+func (m *TokenSet) String() string { return proto.CompactTextString(m) }
+func (*TokenSet) ProtoMessage()    {}
+func (*TokenSet) Descriptor() ([]byte, []int) {
+	return fileDescriptor_9ea8707737c33b38, []int{0}
+}
+func (m *TokenSet) XXX_Unmarshal(b []byte) error {
+	return m.Unmarshal(b)
+}
+func (m *TokenSet) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	if deterministic {
+		return xxx_messageInfo_TokenSet.Marshal(b, m, deterministic)
+	} else {
+		b = b[:cap(b)]
+		n, err := m.MarshalToSizedBuffer(b)
+		if err != nil {
+			return nil, err
+		}
+		return b[:n], nil
+	}
+}
+func (m *TokenSet) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_TokenSet.Merge(m, src)
+}
+func (m *TokenSet) XXX_Size() int {
+	return m.ProtoSize()
+}
+func (m *TokenSet) XXX_DiscardUnknown() {
+	xxx_messageInfo_TokenSet.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_TokenSet proto.InternalMessageInfo
+
+func init() {
+	proto.RegisterType((*TokenSet)(nil), "api.TokenSet")
+	proto.RegisterMapType((map[string]int64)(nil), "api.TokenSet.TokensEntry")
+}
+
+func init() { proto.RegisterFile("lib/api/tokenset.proto", fileDescriptor_9ea8707737c33b38) }
+
+var fileDescriptor_9ea8707737c33b38 = []byte{
+	// 260 bytes of a gzipped FileDescriptorProto
+	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xe2, 0x12, 0xcb, 0xc9, 0x4c, 0xd2,
+	0x4f, 0x2c, 0xc8, 0xd4, 0x2f, 0xc9, 0xcf, 0x4e, 0xcd, 0x2b, 0x4e, 0x2d, 0xd1, 0x2b, 0x28, 0xca,
+	0x2f, 0xc9, 0x17, 0x62, 0x4e, 0x2c, 0xc8, 0x54, 0x3a, 0xce, 0xc8, 0xc5, 0x11, 0x02, 0x12, 0x0f,
+	0x4e, 0x2d, 0x11, 0x0a, 0xe0, 0x62, 0x83, 0xa8, 0x91, 0x60, 0x54, 0x60, 0xd6, 0xe0, 0x36, 0x92,
+	0xd4, 0x4b, 0x2c, 0xc8, 0xd4, 0x83, 0x49, 0x43, 0x18, 0xc5, 0xae, 0x79, 0x25, 0x45, 0x95, 0x4e,
+	0xb2, 0x27, 0xee, 0xc9, 0x33, 0xbc, 0xba, 0x27, 0x0f, 0xd5, 0xf0, 0xe9, 0x9e, 0x3c, 0x77, 0x45,
+	0x6e, 0x8e, 0x95, 0x12, 0x98, 0xab, 0x14, 0x04, 0x15, 0x96, 0xca, 0xe4, 0xe2, 0x46, 0xd2, 0x25,
+	0xa4, 0xc6, 0xc5, 0x9c, 0x9d, 0x5a, 0x29, 0xc1, 0xa8, 0xc0, 0xa8, 0xc1, 0xe9, 0x24, 0xf2, 0xea,
+	0x9e, 0x3c, 0x88, 0xfb, 0xe9, 0x9e, 0x3c, 0x27, 0x58, 0x6f, 0x76, 0x6a, 0xa5, 0x52, 0x10, 0x48,
+	0x44, 0x48, 0x8f, 0x8b, 0xb5, 0x2c, 0x31, 0xa7, 0x34, 0x55, 0x82, 0x49, 0x81, 0x51, 0x83, 0xd9,
+	0x49, 0xe2, 0xd5, 0x3d, 0x79, 0x88, 0x00, 0xdc, 0x1e, 0x30, 0x4f, 0x29, 0x08, 0x22, 0x6a, 0xc5,
+	0x64, 0xc1, 0xe8, 0xe4, 0x71, 0xe2, 0xa1, 0x1c, 0xc3, 0x85, 0x87, 0x72, 0x0c, 0x27, 0x1e, 0xc9,
+	0x31, 0x5e, 0x78, 0x24, 0xc7, 0x38, 0xe1, 0xb1, 0x1c, 0xc3, 0x82, 0xc7, 0x72, 0x8c, 0x17, 0x1e,
+	0xcb, 0x31, 0xdc, 0x78, 0x2c, 0xc7, 0x10, 0xa5, 0x96, 0x9e, 0x59, 0x92, 0x51, 0x9a, 0xa4, 0x97,
+	0x9c, 0x9f, 0xab, 0x5f, 0x5c, 0x99, 0x97, 0x5c, 0x92, 0x91, 0x99, 0x97, 0x8e, 0xc4, 0x82, 0x86,
+	0x53, 0x12, 0x1b, 0x38, 0x7c, 0x8c, 0x01, 0x01, 0x00, 0x00, 0xff, 0xff, 0xfe, 0x25, 0x31, 0x49,
+	0x39, 0x01, 0x00, 0x00,
+}
+
+func (m *TokenSet) Marshal() (dAtA []byte, err error) {
+	size := m.ProtoSize()
+	dAtA = make([]byte, size)
+	n, err := m.MarshalToSizedBuffer(dAtA[:size])
+	if err != nil {
+		return nil, err
+	}
+	return dAtA[:n], nil
+}
+
+func (m *TokenSet) MarshalTo(dAtA []byte) (int, error) {
+	size := m.ProtoSize()
+	return m.MarshalToSizedBuffer(dAtA[:size])
+}
+
+func (m *TokenSet) MarshalToSizedBuffer(dAtA []byte) (int, error) {
+	i := len(dAtA)
+	_ = i
+	var l int
+	_ = l
+	if len(m.Tokens) > 0 {
+		for k := range m.Tokens {
+			v := m.Tokens[k]
+			baseI := i
+			i = encodeVarintTokenset(dAtA, i, uint64(v))
+			i--
+			dAtA[i] = 0x10
+			i -= len(k)
+			copy(dAtA[i:], k)
+			i = encodeVarintTokenset(dAtA, i, uint64(len(k)))
+			i--
+			dAtA[i] = 0xa
+			i = encodeVarintTokenset(dAtA, i, uint64(baseI-i))
+			i--
+			dAtA[i] = 0xa
+		}
+	}
+	return len(dAtA) - i, nil
+}
+
+func encodeVarintTokenset(dAtA []byte, offset int, v uint64) int {
+	offset -= sovTokenset(v)
+	base := offset
+	for v >= 1<<7 {
+		dAtA[offset] = uint8(v&0x7f | 0x80)
+		v >>= 7
+		offset++
+	}
+	dAtA[offset] = uint8(v)
+	return base
+}
+func (m *TokenSet) ProtoSize() (n int) {
+	if m == nil {
+		return 0
+	}
+	var l int
+	_ = l
+	if len(m.Tokens) > 0 {
+		for k, v := range m.Tokens {
+			_ = k
+			_ = v
+			mapEntrySize := 1 + len(k) + sovTokenset(uint64(len(k))) + 1 + sovTokenset(uint64(v))
+			n += mapEntrySize + 1 + sovTokenset(uint64(mapEntrySize))
+		}
+	}
+	return n
+}
+
+func sovTokenset(x uint64) (n int) {
+	return (math_bits.Len64(x|1) + 6) / 7
+}
+func sozTokenset(x uint64) (n int) {
+	return sovTokenset(uint64((x << 1) ^ uint64((int64(x) >> 63))))
+}
+func (m *TokenSet) Unmarshal(dAtA []byte) error {
+	l := len(dAtA)
+	iNdEx := 0
+	for iNdEx < l {
+		preIndex := iNdEx
+		var wire uint64
+		for shift := uint(0); ; shift += 7 {
+			if shift >= 64 {
+				return ErrIntOverflowTokenset
+			}
+			if iNdEx >= l {
+				return io.ErrUnexpectedEOF
+			}
+			b := dAtA[iNdEx]
+			iNdEx++
+			wire |= uint64(b&0x7F) << shift
+			if b < 0x80 {
+				break
+			}
+		}
+		fieldNum := int32(wire >> 3)
+		wireType := int(wire & 0x7)
+		if wireType == 4 {
+			return fmt.Errorf("proto: TokenSet: wiretype end group for non-group")
+		}
+		if fieldNum <= 0 {
+			return fmt.Errorf("proto: TokenSet: illegal tag %d (wire type %d)", fieldNum, wire)
+		}
+		switch fieldNum {
+		case 1:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field Tokens", wireType)
+			}
+			var msglen int
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowTokenset
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				msglen |= int(b&0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			if msglen < 0 {
+				return ErrInvalidLengthTokenset
+			}
+			postIndex := iNdEx + msglen
+			if postIndex < 0 {
+				return ErrInvalidLengthTokenset
+			}
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			if m.Tokens == nil {
+				m.Tokens = make(map[string]int64)
+			}
+			var mapkey string
+			var mapvalue int64
+			for iNdEx < postIndex {
+				entryPreIndex := iNdEx
+				var wire uint64
+				for shift := uint(0); ; shift += 7 {
+					if shift >= 64 {
+						return ErrIntOverflowTokenset
+					}
+					if iNdEx >= l {
+						return io.ErrUnexpectedEOF
+					}
+					b := dAtA[iNdEx]
+					iNdEx++
+					wire |= uint64(b&0x7F) << shift
+					if b < 0x80 {
+						break
+					}
+				}
+				fieldNum := int32(wire >> 3)
+				if fieldNum == 1 {
+					var stringLenmapkey uint64
+					for shift := uint(0); ; shift += 7 {
+						if shift >= 64 {
+							return ErrIntOverflowTokenset
+						}
+						if iNdEx >= l {
+							return io.ErrUnexpectedEOF
+						}
+						b := dAtA[iNdEx]
+						iNdEx++
+						stringLenmapkey |= uint64(b&0x7F) << shift
+						if b < 0x80 {
+							break
+						}
+					}
+					intStringLenmapkey := int(stringLenmapkey)
+					if intStringLenmapkey < 0 {
+						return ErrInvalidLengthTokenset
+					}
+					postStringIndexmapkey := iNdEx + intStringLenmapkey
+					if postStringIndexmapkey < 0 {
+						return ErrInvalidLengthTokenset
+					}
+					if postStringIndexmapkey > l {
+						return io.ErrUnexpectedEOF
+					}
+					mapkey = string(dAtA[iNdEx:postStringIndexmapkey])
+					iNdEx = postStringIndexmapkey
+				} else if fieldNum == 2 {
+					for shift := uint(0); ; shift += 7 {
+						if shift >= 64 {
+							return ErrIntOverflowTokenset
+						}
+						if iNdEx >= l {
+							return io.ErrUnexpectedEOF
+						}
+						b := dAtA[iNdEx]
+						iNdEx++
+						mapvalue |= int64(b&0x7F) << shift
+						if b < 0x80 {
+							break
+						}
+					}
+				} else {
+					iNdEx = entryPreIndex
+					skippy, err := skipTokenset(dAtA[iNdEx:])
+					if err != nil {
+						return err
+					}
+					if (skippy < 0) || (iNdEx+skippy) < 0 {
+						return ErrInvalidLengthTokenset
+					}
+					if (iNdEx + skippy) > postIndex {
+						return io.ErrUnexpectedEOF
+					}
+					iNdEx += skippy
+				}
+			}
+			m.Tokens[mapkey] = mapvalue
+			iNdEx = postIndex
+		default:
+			iNdEx = preIndex
+			skippy, err := skipTokenset(dAtA[iNdEx:])
+			if err != nil {
+				return err
+			}
+			if (skippy < 0) || (iNdEx+skippy) < 0 {
+				return ErrInvalidLengthTokenset
+			}
+			if (iNdEx + skippy) > l {
+				return io.ErrUnexpectedEOF
+			}
+			iNdEx += skippy
+		}
+	}
+
+	if iNdEx > l {
+		return io.ErrUnexpectedEOF
+	}
+	return nil
+}
+func skipTokenset(dAtA []byte) (n int, err error) {
+	l := len(dAtA)
+	iNdEx := 0
+	depth := 0
+	for iNdEx < l {
+		var wire uint64
+		for shift := uint(0); ; shift += 7 {
+			if shift >= 64 {
+				return 0, ErrIntOverflowTokenset
+			}
+			if iNdEx >= l {
+				return 0, io.ErrUnexpectedEOF
+			}
+			b := dAtA[iNdEx]
+			iNdEx++
+			wire |= (uint64(b) & 0x7F) << shift
+			if b < 0x80 {
+				break
+			}
+		}
+		wireType := int(wire & 0x7)
+		switch wireType {
+		case 0:
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return 0, ErrIntOverflowTokenset
+				}
+				if iNdEx >= l {
+					return 0, io.ErrUnexpectedEOF
+				}
+				iNdEx++
+				if dAtA[iNdEx-1] < 0x80 {
+					break
+				}
+			}
+		case 1:
+			iNdEx += 8
+		case 2:
+			var length int
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return 0, ErrIntOverflowTokenset
+				}
+				if iNdEx >= l {
+					return 0, io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				length |= (int(b) & 0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			if length < 0 {
+				return 0, ErrInvalidLengthTokenset
+			}
+			iNdEx += length
+		case 3:
+			depth++
+		case 4:
+			if depth == 0 {
+				return 0, ErrUnexpectedEndOfGroupTokenset
+			}
+			depth--
+		case 5:
+			iNdEx += 4
+		default:
+			return 0, fmt.Errorf("proto: illegal wireType %d", wireType)
+		}
+		if iNdEx < 0 {
+			return 0, ErrInvalidLengthTokenset
+		}
+		if depth == 0 {
+			return iNdEx, nil
+		}
+	}
+	return 0, io.ErrUnexpectedEOF
+}
+
+var (
+	ErrInvalidLengthTokenset        = fmt.Errorf("proto: negative length found during unmarshaling")
+	ErrIntOverflowTokenset          = fmt.Errorf("proto: integer overflow")
+	ErrUnexpectedEndOfGroupTokenset = fmt.Errorf("proto: unexpected end of group")
+)
diff --git a/lib/locations/locations.go b/lib/locations/locations.go
index e384b897a..ad92124a6 100644
--- a/lib/locations/locations.go
+++ b/lib/locations/locations.go
@@ -29,7 +29,6 @@ const (
 	HTTPSKeyFile  LocationEnum = "httpsKeyFile"
 	Database      LocationEnum = "database"
 	LogFile       LocationEnum = "logFile"
-	CsrfTokens    LocationEnum = "csrfTokens"
 	PanicLog      LocationEnum = "panicLog"
 	AuditLog      LocationEnum = "auditLog"
 	GUIAssets     LocationEnum = "guiAssets"
@@ -121,7 +120,6 @@ var locationTemplates = map[LocationEnum]string{
 	HTTPSKeyFile:  "${config}/https-key.pem",
 	Database:      "${data}/" + LevelDBDir,
 	LogFile:       "${data}/syncthing.log", // --logfile on Windows
-	CsrfTokens:    "${data}/csrftokens.txt",
 	PanicLog:      "${data}/panic-%{timestamp}.log",
 	AuditLog:      "${data}/audit-%{timestamp}.log",
 	GUIAssets:     "${config}/gui",
@@ -170,7 +168,6 @@ func PrettyPaths() string {
 	fmt.Fprintf(&b, "Database location:\n\t%s\n\n", Get(Database))
 	fmt.Fprintf(&b, "Log file:\n\t%s\n\n", Get(LogFile))
 	fmt.Fprintf(&b, "GUI override directory:\n\t%s\n\n", Get(GUIAssets))
-	fmt.Fprintf(&b, "CSRF tokens file:\n\t%s\n\n", Get(CsrfTokens))
 	fmt.Fprintf(&b, "Default sync folder directory:\n\t%s\n\n", Get(DefFolder))
 	return b.String()
 }
diff --git a/lib/syncthing/syncthing.go b/lib/syncthing/syncthing.go
index 237131521..fd627b581 100644
--- a/lib/syncthing/syncthing.go
+++ b/lib/syncthing/syncthing.go
@@ -305,7 +305,7 @@ func (a *App) startup() error {
 
 	// GUI
 
-	if err := a.setupGUI(m, defaultSub, diskSub, discoveryManager, connectionsService, usageReportingSvc, errors, systemLog); err != nil {
+	if err := a.setupGUI(m, defaultSub, diskSub, discoveryManager, connectionsService, usageReportingSvc, errors, systemLog, miscDB); err != nil {
 		l.Warnln("Failed starting API:", err)
 		return err
 	}
@@ -407,7 +407,7 @@ func (a *App) stopWithErr(stopReason svcutil.ExitStatus, err error) svcutil.Exit
 	return a.exitStatus
 }
 
-func (a *App) setupGUI(m model.Model, defaultSub, diskSub events.BufferedSubscription, discoverer discover.Manager, connectionsService connections.Service, urService *ur.Service, errors, systemLog logger.Recorder) error {
+func (a *App) setupGUI(m model.Model, defaultSub, diskSub events.BufferedSubscription, discoverer discover.Manager, connectionsService connections.Service, urService *ur.Service, errors, systemLog logger.Recorder, miscDB *db.NamespacedKV) error {
 	guiCfg := a.cfg.GUI()
 
 	if !guiCfg.Enabled {
@@ -421,7 +421,7 @@ func (a *App) setupGUI(m model.Model, defaultSub, diskSub events.BufferedSubscri
 	summaryService := model.NewFolderSummaryService(a.cfg, m, a.myID, a.evLogger)
 	a.mainService.Add(summaryService)
 
-	apiSvc := api.New(a.myID, a.cfg, locations.Get(locations.GUIAssets), tlsDefaultCommonName, m, defaultSub, diskSub, a.evLogger, discoverer, connectionsService, urService, summaryService, errors, systemLog, a.opts.NoUpgrade)
+	apiSvc := api.New(a.myID, a.cfg, locations.Get(locations.GUIAssets), tlsDefaultCommonName, m, defaultSub, diskSub, a.evLogger, discoverer, connectionsService, urService, summaryService, errors, systemLog, a.opts.NoUpgrade, miscDB)
 	a.mainService.Add(apiSvc)
 
 	if err := apiSvc.WaitForStart(); err != nil {
diff --git a/proto/generate.go b/proto/generate.go
index 03be4522e..c264868d8 100644
--- a/proto/generate.go
+++ b/proto/generate.go
@@ -26,7 +26,7 @@ import (
 
 // Inception, go generate calls the script itself that then deals with generation.
 // This is only done because go:generate does not support wildcards in paths.
-//go:generate go run generate.go lib/protocol lib/config lib/fs lib/db lib/discover
+//go:generate go run generate.go lib/protocol lib/config lib/fs lib/db lib/discover lib/api
 
 func main() {
 	for _, path := range os.Args[1:] {
diff --git a/proto/lib/api/tokenset.proto b/proto/lib/api/tokenset.proto
new file mode 100644
index 000000000..bf3ff0842
--- /dev/null
+++ b/proto/lib/api/tokenset.proto
@@ -0,0 +1,8 @@
+syntax = "proto3";
+
+package api;
+
+message TokenSet {
+    // token -> expiry time (epoch nanoseconds)
+    map<string, int64> tokens = 1;
+}