[SECURITY] Rework long-term authentication

- This is a 'front-port' of the already existing patch on v1.21 and
v1.20, but applied on top of what Gitea has done to rework the LTA
mechanism. Forgejo will stick with the reworked mechanism by the Forgejo
Security team for the time being. The removal of legacy code (AES-GCM) has been
left out.
- The current architecture is inherently insecure, because you can
construct the 'secret' cookie value with values that are available in
the database. Thus provides zero protection when a database is
dumped/leaked.
- This patch implements a new architecture that's inspired from: [Paragonie Initiative](https://paragonie.com/blog/2015/04/secure-authentication-php-with-long-term-persistence#secure-remember-me-cookies).
- Integration testing is added to ensure the new mechanism works.
- Removes a setting, because it's not used anymore.

routers/install/install.go

@@ -27,14 +27,12 @@ import (
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/templates"
-	"code.gitea.io/gitea/modules/timeutil"
 	"code.gitea.io/gitea/modules/translation"
 	"code.gitea.io/gitea/modules/user"
 	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/modules/web"
 	"code.gitea.io/gitea/modules/web/middleware"
 	"code.gitea.io/gitea/routers/common"
-	auth_service "code.gitea.io/gitea/services/auth"
 	"code.gitea.io/gitea/services/forms"
 
 	"gitea.com/go-chi/session"
@@ -549,20 +547,13 @@ func SubmitInstall(ctx *context.Context) {
 			u, _ = user_model.GetUserByName(ctx, u.Name)
 		}
 
-		nt, token, err := auth_service.CreateAuthTokenForUserID(ctx, u.ID)
-		if err != nil {
-			ctx.ServerError("CreateAuthTokenForUserID", err)
-			return
-		}
-
-		ctx.SetSiteCookie(setting.CookieRememberName, nt.ID+":"+token, setting.LogInRememberDays*timeutil.Day)
-
-		// Auto-login for admin
-		if err = ctx.Session.Set("uid", u.ID); err != nil {
+		if err := ctx.SetLTACookie(u); err != nil {
 			ctx.RenderWithErr(ctx.Tr("install.save_config_failed", err), tplInstall, &form)
 			return
 		}
-		if err = ctx.Session.Set("uname", u.Name); err != nil {
+
+		// Auto-login for admin
+		if err = ctx.Session.Set("uid", u.ID); err != nil {
 			ctx.RenderWithErr(ctx.Tr("install.save_config_failed", err), tplInstall, &form)
 			return
 		}

routers/web/auth/auth.go

@@ -5,6 +5,8 @@
 package auth
 
 import (
+	"crypto/subtle"
+	"encoding/hex"
 	"errors"
 	"fmt"
 	"net/http"
@@ -56,23 +58,39 @@ func autoSignIn(ctx *context.Context) (bool, error) {
 		}
 	}()
 
-	if err := auth.DeleteExpiredAuthTokens(ctx); err != nil {
-		log.Error("Failed to delete expired auth tokens: %v", err)
+	authCookie := ctx.GetSiteCookie(setting.CookieRememberName)
+	if len(authCookie) == 0 {
+		return false, nil
 	}
 
-	t, err := auth_service.CheckAuthToken(ctx, ctx.GetSiteCookie(setting.CookieRememberName))
+	lookupKey, validator, found := strings.Cut(authCookie, ":")
+	if !found {
+		return false, nil
+	}
+
+	authToken, err := auth.FindAuthToken(ctx, lookupKey)
 	if err != nil {
-		switch err {
-		case auth_service.ErrAuthTokenInvalidFormat, auth_service.ErrAuthTokenExpired:
+		if errors.Is(err, util.ErrNotExist) {
 			return false, nil
 		}
 		return false, err
 	}
-	if t == nil {
+
+	if authToken.IsExpired() {
+		err = auth.DeleteAuthToken(ctx, authToken)
+		return false, err
+	}
+
+	rawValidator, err := hex.DecodeString(validator)
+	if err != nil {
+		return false, err
+	}
+
+	if subtle.ConstantTimeCompare([]byte(authToken.HashedValidator), []byte(auth.HashValidator(rawValidator))) == 0 {
 		return false, nil
 	}
 
-	u, err := user_model.GetUserByID(ctx, t.UserID)
+	u, err := user_model.GetUserByID(ctx, authToken.UID)
 	if err != nil {
 		if !user_model.IsErrUserNotExist(err) {
 			return false, fmt.Errorf("GetUserByID: %w", err)
@@ -82,17 +100,9 @@ func autoSignIn(ctx *context.Context) (bool, error) {
 
 	isSucceed = true
 
-	nt, token, err := auth_service.RegenerateAuthToken(ctx, t)
-	if err != nil {
-		return false, err
-	}
-
-	ctx.SetSiteCookie(setting.CookieRememberName, nt.ID+":"+token, setting.LogInRememberDays*timeutil.Day)
-
 	if err := updateSession(ctx, nil, map[string]any{
 		// Set session IDs
-		"uid":   u.ID,
-		"uname": u.Name,
+		"uid": u.ID,
 	}); err != nil {
 		return false, fmt.Errorf("unable to updateSession: %w", err)
 	}
@@ -128,10 +138,6 @@ func CheckAutoLogin(ctx *context.Context) bool {
 	// Check auto-login
 	isSucceed, err := autoSignIn(ctx)
 	if err != nil {
-		if errors.Is(err, auth_service.ErrAuthTokenInvalidHash) {
-			ctx.Flash.Error(ctx.Tr("auth.remember_me.compromised"), true)
-			return false
-		}
 		ctx.ServerError("autoSignIn", err)
 		return true
 	}
@@ -302,13 +308,10 @@ func handleSignIn(ctx *context.Context, u *user_model.User, remember bool) {
 
 func handleSignInFull(ctx *context.Context, u *user_model.User, remember, obeyRedirect bool) string {
 	if remember {
-		nt, token, err := auth_service.CreateAuthTokenForUserID(ctx, u.ID)
-		if err != nil {
-			ctx.ServerError("CreateAuthTokenForUserID", err)
+		if err := ctx.SetLTACookie(u); err != nil {
+			ctx.ServerError("GenerateAuthToken", err)
 			return setting.AppSubURL + "/"
 		}
-
-		ctx.SetSiteCookie(setting.CookieRememberName, nt.ID+":"+token, setting.LogInRememberDays*timeutil.Day)
 	}
 
 	if err := updateSession(ctx, []string{
@@ -321,8 +324,7 @@ func handleSignInFull(ctx *context.Context, u *user_model.User, remember, obeyRe
 		"twofaRemember",
 		"linkAccount",
 	}, map[string]any{
-		"uid":   u.ID,
-		"uname": u.Name,
+		"uid": u.ID,
 	}); err != nil {
 		ctx.ServerError("RegenerateSession", err)
 		return setting.AppSubURL + "/"
@@ -743,8 +745,7 @@ func handleAccountActivation(ctx *context.Context, user *user_model.User) {
 	log.Trace("User activated: %s", user.Name)
 
 	if err := updateSession(ctx, nil, map[string]any{
-		"uid":   user.ID,
-		"uname": user.Name,
+		"uid": user.ID,
 	}); err != nil {
 		log.Error("Unable to regenerate session for user: %-v with email: %s: %v", user, user.Email, err)
 		ctx.ServerError("ActivateUserEmail", err)

routers/web/auth/oauth.go

@@ -1118,8 +1118,7 @@ func handleOAuth2SignIn(ctx *context.Context, source *auth.Source, u *user_model
 	// we can't sign the user in just yet. Instead, redirect them to the 2FA authentication page.
 	if !needs2FA {
 		if err := updateSession(ctx, nil, map[string]any{
-			"uid":   u.ID,
-			"uname": u.Name,
+			"uid": u.ID,
 		}); err != nil {
 			ctx.ServerError("updateSession", err)
 			return

routers/web/user/setting/account.go

@@ -78,6 +78,15 @@ func AccountPost(ctx *context.Context) {
 			ctx.ServerError("UpdateUser", err)
 			return
 		}
+
+		// Re-generate LTA cookie.
+		if len(ctx.GetSiteCookie(setting.CookieRememberName)) != 0 {
+			if err := ctx.SetLTACookie(ctx.Doer); err != nil {
+				ctx.ServerError("SetLTACookie", err)
+				return
+			}
+		}
+
 		log.Trace("User password updated: %s", ctx.Doer.Name)
 		ctx.Flash.Success(ctx.Tr("settings.change_password_success"))
 	}