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/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,