fix(auth): atomic refresh rotation and a 7-day absolute session limit

- Rotation claims the old token with a conditional update; of two
  concurrent refreshes only one gets a successor, so a stolen token cannot
  fork into two live sessions.
- A token rotated out less than 10 s ago (parallel tab) is refused without
  revoking every session; later reuse still revokes them all.
- Sessions end at most SESSION_MAX_AGE (default 7 days) after login: the
  login time is inherited by every rotated token and caps its expiry.
- The refresh cookie is cleared with the same attributes it was set with.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

ApiCore-Backend/.env.example

@@ -9,6 +9,8 @@ JWT_ACCESS_SECRET="change-me-to-a-random-value-at-least-32-characters-long"
 JWT_REFRESH_SECRET="change-me-refresh-secret"
 JWT_ACCESS_EXPIRES_IN="15m"
 JWT_REFRESH_EXPIRES_IN="7d"
+# Hard limit from login, however often the session is refreshed.
+SESSION_MAX_AGE="7d"
 
 PORT=3001
 FRONTEND_ORIGIN="http://localhost:3000"

ApiCore-Backend/prisma/migrations/20261001110000_refresh_session_start/migration.sql

@@ -0,0 +1,3 @@
+-- Absolute session lifetime: every rotated refresh token keeps the time
+-- the session was first opened. Existing sessions count from now.
+ALTER TABLE "RefreshToken" ADD COLUMN "sessionStartedAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP;

ApiCore-Backend/prisma/schema.prisma

@@ -161,6 +161,9 @@ model RefreshToken {
   expiresAt DateTime
   createdAt DateTime  @default(now())
   revokedAt DateTime?
+  // Anmeldezeitpunkt der Sitzung, an jede rotierte Nachfolge-Token vererbt:
+  // spaetestens SESSION_MAX_AGE danach ist neu anzumelden.
+  sessionStartedAt DateTime @default(now())
 
   @@index([userId])
 }

ApiCore-Backend/src/auth/auth.service.spec.ts

@@ -323,7 +323,8 @@ describe('AuthService', () => {
       prisma.refreshToken.findUnique.mockResolvedValue({
         id: 'rt-1',
         userId: activeUser.id,
-        revokedAt: new Date(),
+        // Rotated out a minute ago - well past the parallel-tab window.
+        revokedAt: new Date(Date.now() - 60_000),
         expiresAt: new Date(Date.now() + 1000),
       });
       prisma.refreshToken.updateMany.mockResolvedValue({ count: 2 });
@@ -353,22 +354,78 @@ describe('AuthService', () => {
       );
     });
 
+    it('does not revoke everything when a parallel tab just rotated the token', async () => {
+      prisma.refreshToken.findUnique.mockResolvedValue({
+        id: 'rt-1',
+        userId: activeUser.id,
+        revokedAt: new Date(Date.now() - 1000),
+        expiresAt: new Date(Date.now() + 1000),
+      });
+
+      await expect(authService.refresh('just-rotated')).rejects.toBeInstanceOf(
+        UnauthorizedException,
+      );
+      expect(prisma.refreshToken.updateMany).not.toHaveBeenCalled();
+    });
+
+    it('gives only one of two concurrent refreshes a successor', async () => {
+      prisma.refreshToken.findUnique.mockResolvedValue({
+        id: 'rt-1',
+        userId: activeUser.id,
+        revokedAt: null,
+        expiresAt: new Date(Date.now() + 1000),
+        sessionStartedAt: new Date(),
+      });
+      usersService.findById.mockResolvedValue(activeUser);
+      prisma.refreshToken.updateMany.mockResolvedValue({ count: 0 });
+
+      await expect(authService.refresh('raced-token')).rejects.toBeInstanceOf(
+        UnauthorizedException,
+      );
+      expect(prisma.refreshToken.create).not.toHaveBeenCalled();
+    });
+
+    it('never extends a session past seven days from login', async () => {
+      const startedSixDaysAgo = new Date(Date.now() - 6 * 24 * 3600 * 1000);
+      prisma.refreshToken.findUnique.mockResolvedValue({
+        id: 'rt-1',
+        userId: activeUser.id,
+        revokedAt: null,
+        expiresAt: new Date(Date.now() + 1000),
+        sessionStartedAt: startedSixDaysAgo,
+      });
+      usersService.findById.mockResolvedValue(activeUser);
+      prisma.refreshToken.updateMany.mockResolvedValue({ count: 1 });
+      prisma.refreshToken.create.mockResolvedValue({});
+
+      await authService.refresh('valid-token');
+
+      const [[createArg]] = prisma.refreshToken.create.mock.calls as [
+        [{ data: { expiresAt: Date; sessionStartedAt: Date } }],
+      ];
+      expect(createArg.data.sessionStartedAt).toEqual(startedSixDaysAgo);
+      expect(createArg.data.expiresAt.getTime()).toBe(
+        startedSixDaysAgo.getTime() + 7 * 24 * 3600 * 1000,
+      );
+    });
+
     it('rotates the refresh token on success', async () => {
       prisma.refreshToken.findUnique.mockResolvedValue({
         id: 'rt-1',
         userId: activeUser.id,
         revokedAt: null,
         expiresAt: new Date(Date.now() + 1000),
+        sessionStartedAt: new Date(),
       });
       usersService.findById.mockResolvedValue(activeUser);
-      prisma.refreshToken.update.mockResolvedValue({});
+      prisma.refreshToken.updateMany.mockResolvedValue({ count: 1 });
       prisma.refreshToken.create.mockResolvedValue({});
 
       const result = await authService.refresh('valid-token');
 
       expect(result.accessToken).toBe('signed.jwt.token');
-      expect(prisma.refreshToken.update).toHaveBeenCalledWith(
-        expect.objectContaining({ where: { id: 'rt-1' } }),
+      expect(prisma.refreshToken.updateMany).toHaveBeenCalledWith(
+        expect.objectContaining({ where: { id: 'rt-1', revokedAt: null } }),
       );
       expect(auditLog.record).toHaveBeenCalledWith(
         expect.objectContaining({

ApiCore-Backend/src/auth/auth.service.ts

@@ -33,6 +33,12 @@ export interface CurrentUserProfile {
 
 const REFRESH_TOKEN_BYTES = 40;
 
+// Hard cap from the moment of login, however often the session is refreshed.
+const DEFAULT_SESSION_MAX_AGE = '7d';
+// Two tabs refreshing with the same token at the same moment is normal;
+// only a reuse after this window is treated as theft.
+const ROTATION_GRACE_MS = 10_000;
+
 // Same answer for unknown email, wrong password, deactivated or locked
 // account - nothing in the response tells which one it was.
 const INVALID_CREDENTIALS =
@@ -92,14 +98,24 @@ export class AuthService {
     );
   }
 
-  private async issueRefreshToken(userId: string): Promise<string> {
+  private async issueRefreshToken(
+    userId: string,
+    sessionStartedAt: Date = new Date(),
+  ): Promise<string> {
     const token = crypto.randomBytes(REFRESH_TOKEN_BYTES).toString('hex');
-    const expiresAt = new Date(
+    const slidingExpiry =
       Date.now() +
-        parseDurationToMs(process.env.JWT_REFRESH_EXPIRES_IN ?? '7d'),
-    );
+      parseDurationToMs(process.env.JWT_REFRESH_EXPIRES_IN ?? '7d');
+    const absoluteExpiry =
+      sessionStartedAt.getTime() +
+      parseDurationToMs(process.env.SESSION_MAX_AGE ?? DEFAULT_SESSION_MAX_AGE);
     await this.prisma.refreshToken.create({
-      data: { userId, tokenHash: this.hashRefreshToken(token), expiresAt },
+      data: {
+        userId,
+        tokenHash: this.hashRefreshToken(token),
+        expiresAt: new Date(Math.min(slidingExpiry, absoluteExpiry)),
+        sessionStartedAt,
+      },
     });
     return token;
   }
@@ -238,6 +254,14 @@ export class AuthService {
     if (!stored) {
       throw new UnauthorizedException('Invalid refresh token');
     }
+    if (
+      stored.revokedAt &&
+      Date.now() - stored.revokedAt.getTime() < ROTATION_GRACE_MS
+    ) {
+      // Lost a race with a parallel refresh (second tab): no new session,
+      // but no alarm either - that tab simply uses the other's cookie.
+      throw new UnauthorizedException('Invalid refresh token');
+    }
     if (stored.revokedAt) {
       // Reuse of an already-rotated-out refresh token is a strong signal
       // it was stolen (a legitimate client only ever presents the newest
@@ -260,16 +284,25 @@ export class AuthService {
     if (!user.isActive) {
       throw new UnauthorizedException('Invalid refresh token');
     }
-    await this.prisma.refreshToken.update({
-      where: { id: stored.id },
+    // Atomic: of two requests presenting the same token, exactly one wins
+    // and gets a successor - one stolen token can never fork into two live
+    // sessions.
+    const claimed = await this.prisma.refreshToken.updateMany({
+      where: { id: stored.id, revokedAt: null },
       data: { revokedAt: new Date() },
     });
+    if (claimed.count !== 1) {
+      throw new UnauthorizedException('Invalid refresh token');
+    }
     const authenticatedUser = {
       id: user.id,
       email: user.email,
     };
     const accessToken = this.signAccessToken(authenticatedUser);
-    const newRefreshToken = await this.issueRefreshToken(user.id);
+    const newRefreshToken = await this.issueRefreshToken(
+      user.id,
+      stored.sessionStartedAt,
+    );
     await this.auditLog.record({
       entityType: 'AuthSession',
       entityId: user.id,

ApiCore-Backend/src/auth/util/refresh-token-cookie.ts

@@ -5,24 +5,32 @@ import { parseDurationToMs } from './duration';
 export const REFRESH_TOKEN_COOKIE = 'refreshToken';
 export const REFRESH_TOKEN_COOKIE_PATH = '/api/v1/auth';
 
-export function setRefreshTokenCookie(
-  res: Response,
-  refreshToken: string,
-): void {
-  res.cookie(REFRESH_TOKEN_COOKIE, refreshToken, {
+function cookieOptions() {
+  return {
     httpOnly: true,
     // Explicit opt-out for local HTTP dev only; every real deployment must
     // set COOKIE_SECURE=true so the refresh-token cookie is never sent
     // over plaintext HTTP.
     secure: process.env.COOKIE_SECURE !== 'false',
-    sameSite: 'lax',
+    sameSite: 'lax' as const,
     path: REFRESH_TOKEN_COOKIE_PATH,
+  };
+}
+
+export function setRefreshTokenCookie(
+  res: Response,
+  refreshToken: string,
+): void {
+  res.cookie(REFRESH_TOKEN_COOKIE, refreshToken, {
+    ...cookieOptions(),
     maxAge: parseDurationToMs(process.env.JWT_REFRESH_EXPIRES_IN ?? '7d'),
   });
 }
 
+// Same attributes as when set - some browsers keep a cookie that is
+// cleared with different ones.
 export function clearRefreshTokenCookie(res: Response): void {
-  res.clearCookie(REFRESH_TOKEN_COOKIE, { path: REFRESH_TOKEN_COOKIE_PATH });
+  res.clearCookie(REFRESH_TOKEN_COOKIE, cookieOptions());
 }
 
 export function extractRefreshToken(req: Request): string {