signUpOrIn abstract method
Authenticates an existing user if one exists or creates a new one.
A new passkey will be created if the user identified by loginId
doesn't already exist,
otherwise a passkey must be available on their device to authenticate with.
This function will only return an AuthenticationResponse successfully after the user
identified by loginId
uses their existing passkey on their device or creates a new
one, if the user is being created.
Implementation
Future<AuthenticationResponse> signUpOrIn({required String loginId, SignInOptions? options});