Our iOS app uses Sign in with Apple to authenticate users, and we use Firebase for the backend — for both Auth and Storage. If anyone can provide guidance and/or share experience on how to migrate an iOS app to a different App Store Connect team, particularly with a Firebase backend, that would be fantastic. Below I'll provide info about our situation, and I'll describe what I understand so far about the migration process.
About our app: A few months ago, we transferred our iOS app to a different App Store Connect team, and it seemed that everything was fine... but recently we learned that we should have migrated SIWA (Sign in with Apple) users so that Sign in with Apple will continue to work under the new team, but we didn't do that, and as a result of missing the 60-day window, Apple's documentation says that we now need to transfer the app back to the original team... and then we can start preparing to migrate the SIWA users to the new team.
Before transferring back to the original team, we started receiving errors during the Sign in with Apple process which say "Sign Up Not Completed" in Apple's UI... but the callback authorizationController(controller:didCompleteWithError:) is NOT called.
For reference, here's Apple's documentation on this subject:
TN3159: Migrating Sign in with Apple users for an app transfer
[https://developer.apple.com/documentation/technotes/tn3159-migrating-sign-in-with-apple-users-for-an-app-transfer][2]
Transferring your apps and users to another team
[https://developer.apple.com/documentation/signinwithapple/transferring-your-apps-and-users-to-another-team][3]
Bringing new apps and users into your team
[https://developer.apple.com/documentation/signinwithapple/bringing-new-apps-and-users-into-your-team][4]
Note: the first article contains 4 broken links (thanks Apple 🙄) but it's pretty clear that these 2 other links ☝️ are where those broken links should be pointing to.
In our situation, it's clear that we need to transfer the app back to the original team. But how to proceed after that? As I understand it, for a given user, Apple provides a sub which is basically a user ID that is specific to that team. After the app is transferred to the new team, the sub returned from Apple will be different... but Firebase doesn't appear to store the sub anywhere, so it's either unimportant OR we need to set up our own Auth instead of using Firebase Auth. Thoughts?
When using Sign in with Apple, the user's email address is exposed to our app... but if the user opted to use a private relay email address, that's a problem, because private relay email addresses are ALSO specific to that team. If the user with a private relay email tries to log in under the new team, we won't recognize their "new" email address, but we need a way to associate that user with their "old" account in Firebase.
The solution provided by Apple is that we need to request the transfer_sub (also known as a "transfer identifier") for each user, and we need to store the transfer_sub in our backend to be able to allow a user who is logging in under the new team to still have access to their "old" account in Firebase. Even though private email relay addresses and subs will be different under the new App Store Connect team, the transfer_sub is the same for each user across both teams.
According to Apple's documentation, the user's sub is needed in order to request the transfer_sub... but if we're not already storing the sub in Firebase, then how do we request the sub for every user, then the transfer_sub for every user, and then store that info in Firebase? Does this need to happen on the iOS side? And what would happen to a user who was using our app for months, then stopped using the app for >60 days while we were doing the migration, and then tried to sign in again? Will that user be permanently be locked out of our app? Is it impossible to keep all users happy and able to log into their accounts in this scenario?
TLDR: We're trying to migrate an iOS app with a Firebase backend (Auth and Storage) to a different App Store Connect team... and it's apparently a complicated process because we're using Sign in with Apple. Please help if you can! Thank you! 🙏