Persistent internal-error from getIdToken(true) on iOS App Resume for Apple Sign-In Users, Even After Successful reauthenticateWithCredential

[eternistarr]

We are experiencing a persistent issue on iOS with Firebase Authentication for users signed in via Apple. When the app resumes after being backgrounded (especially after a period that could simulate deep sleep), calling FirebaseAuth.instance.currentUser.getIdToken(true) consistently fails with a [firebase_auth/internal-error]. The full error message is typically: An internal error has occurred, print and inspect the error details for more information.

We attempted a recovery flow where, upon encountering this internal-error for an Apple Sign-In user, we:

Successfully obtained fresh Apple credentials using SignInWithApple.getAppleIDCredential().
Created a new OAuthCredential for Firebase using these Apple credentials.
Successfully called FirebaseAuth.instance.currentUser.reauthenticateWithCredential() with the new Firebase OAuthCredential. This call reports success, and logs indicate the Firebase token is updated (e.g., [FirebaseAuth][I-AUT000017] Has valid access token. Estimated expiration date: <new_future_date>).
However, despite this successful re-authentication sequence, on the very next app resume (even if it occurs within seconds), the call to FirebaseAuth.instance.currentUser.getIdToken(true) again fails with the same [firebase_auth/internal-error]. This creates a situation where the session remains unstable, leading to the user being signed out to prevent an infinite loop of re-authentication prompts if we were to retry the Apple Sign-In flow.

Here's a condensed log sequence illustrating one cycle of this problem after a successful sign-in:

flutter: [AuthWrapper] App resumed on ios.
flutter: [AuthWrapper] iOS: Delay complete. Processing resume for user <USER_UID>.
flutter: [FirebaseAuth][I-AUT000017] Fetching new token from backend.
flutter: [AuthWrapper] iOS: Error during direct ID token refresh: Code: internal-error, Message: An internal error has occurred, print and inspect the error details for more information.
flutter: [AuthWrapper] iOS: User signed in with Apple: true
flutter: [AuthWrapper] iOS: Attempting Apple re-authentication due to internal-error.
flutter: [AuthService] reauthenticateWithAppleSignIn: Starting Apple Sign-In for re-authentication.
...
flutter: [AuthService] reauthenticateWithAppleSignIn: Successfully obtained Apple credentials.
flutter: [AuthService] reauthenticateWithAppleSignIn: Attempting Firebase re-authentication for user <USER_UID>.
...
11.13.0 - [FirebaseAuth][I-AUT000017] Has valid access token. Estimated expiration date: <NEW_EXPIRY_TIME_AFTER_REAUTH>, current date: <CURRENT_TIME>
flutter: [AuthService] reauthenticateWithAppleSignIn: Firebase re-authentication successful.
flutter: AuthService: User reloaded successfully.
flutter: [AuthWrapper] iOS: Apple re-authentication successful. User session restored.

// On IMMEDIATE NEXT APP RESUME (simulated by backgrounding/foregrounding quickly)
flutter: [AuthWrapper] App resumed on ios.
flutter: [AuthWrapper] iOS: Delay complete. Processing resume for user <USER_UID>.
flutter: [FirebaseAuth][I-AUT000017] Fetching new token from backend.
flutter: [AuthWrapper] iOS: Error during direct ID token refresh: Code: internal-error, Message: An internal error has occurred, print and inspect the error details for more information.
// (At this point, our app signs the user out to prevent a loop if the re-auth was recent)
This behavior suggests that reauthenticateWithCredential for Apple Sign-In users on iOS might not be fully stabilizing the session against this particular internal-error when getIdToken(true) is subsequently called on app resume. The initial sign-in with Apple works perfectly and results in a stable session until the app is backgrounded and resumed after some time. Any insights or guidance on why a successful re-authentication doesn't prevent the immediate recurrence of this internal-error would be greatly appreciated.

Issue Occurs on simulator and physical devices.

Packages in use:
firebase_core: ^3.14.0
firebase_auth: ^5.6.0
cloud_firestore: ^5.6.9
firebase_storage: ^12.4.7