I do wonder, though, whether the requirement for Sign in with Apple is coming in a few years. As in, if you allow users to sign in with email/password, you must allow users to sign in with "sign in with apple". It might be more subtle, like suggested auto-fill to create a new account.
That sounds like a bridge too far even by Apple standards. I can get on board with "if you support Facebook, you have to support us as well", but not allowing any kind of escape hatch feels particularly scummy. At some point it's none of Apple's business how people sign up with my service.
I don't understand how "if you support Facebook, you have to support us as well" is ok. Only by holding the relationship between the user and the developer "hostage".
