Fitbit OAuth Login Loop for Google-based Accounts (No Email/Password)

Users who created their Fitbit account using “Continue with Google” and do not have a Fitbit email/password are unable to complete authentication in our mobile app.

During Fitbit OAuth:

1. User selects Continue with Google
2. Google account is selected successfully
3. Flow redirects back to Fitbit sign-in screen
4. Login enters an infinite loop , OAuth never completes and access tokens are not issued

https://github.com/user-attachments/assets/c40c6eb9-3ba9-4fd0-8f3a-81c08e5fd35d

This behavior is consistent and reproducible.