linkExistingUserWithCredentials method
Starts a OAuth sign-in flow for provider
using Firebase. The instance of FirebaseAuth will be from the default Firebase App
Unless withApp is used to build an instance.
The credentials will be added to the existing Firebase User
An error will be throw if there's no Firebase User
Implementation
@override
Future<User?> linkExistingUserWithCredentials(
String provider, List<String> scopes,
[Map<String, String>? customOAuthParameters]) =>
_delegate.linkExistingUserWithCredentials(
provider, scopes, customOAuthParameters);