I'm planning to transfer my app that uses Sign in with Apple from one development team to another (both are mine). I read https://developer.apple.com/documentation/sign_in_with_apple/transferring_your_apps_and_users_to_another_team and https://developer.apple.com/documentation/sign_in_with_apple/bringing_new_apps_and_users_into_your_team but still don't understand what the migration process should look like.
At first I thought that I could exchange the identifiers for all my users on my backend's side (using /auth/usermigrationinfo), right after the transfer is completed. The problem I see is that in this case my app won't be informed about the new user identifier. I store it in a device's Keychain because I need it later to check the credential state via https://developer.apple.com/documentation/authenticationservices/asauthorizationappleidprovider/3175423-getcredentialstate. If I've understood correclty, this method, called with the "old" user identifier param, after 60 days, starts returning an error or the notFound state. So I have to update this at some point. Okay, the second idea is to re-log silently all my users when they run my app after the transfer (as described at the bottom of this article: https://developer.apple.com/documentation/sign_in_with_apple/bringing_new_apps_and_users_into_your_team). But I can see another problem in here: someone may not run my app within 60 days.
How should I approach this problem? I think this can be quite a common issue for a lot of developers.
Thomas