We have a game that's launched on iOS and we're working on readying the game on Android.
On iOS, we do an initial login with the device ID, and we offer users the possibility of signing in with Apple, at which point we link that Apple account to the existing PlayFab account.
We're taking a similar approach with Android, offering signin to Google Play Services.
One more thing to know is that we have a separate title on PlayFab for testing. Through the game's development (before we added PlayFab) we have used a separate app identifier / bundle ID - sometimes referred to as a 'flavor' - for development versions. We maintain that with PlayFab for various reasons, including that we don't want to contaminate leaderboards with test data, and we want to be able to unlink accounts for testing various situations without fear of harming real users. Of course we still do some minimal testing on the production environment to confirm that it's configured correctly.
The problem is that if a tester has signed in with Google using the test bundle ID/title, repeating the process with the real ID/title fails - "That account is already linked to a different user".
We may need to use different Google accounts to guarantee uniqueness and avoid the two titles interfering with each other in this way. Are there other approaches we could take?
I understand the benefit of trying to identify a user across titles, but it seems that device IDs on iOS & Android, and Sign In With Apple identities are already 'uniquified' to prevent that. If we did have multiple live titles and a user had created separate device ID accounts for each, and later chose to sign in with Google for each, how should we handle it?