signInWithApple method
Implementation
Future<void> signInWithApple() async {
_updateState(const AuthState.loading());
try {
verbose('Signing in with Apple...');
final _OAuthProvider provider = _OAuthProvider('apple.com');
await _firebase.auth().signInWithPopup(provider).toDart;
} catch (e) {
error('Apple sign-in failed: $e');
_updateState(AuthState.withError(_parseFirebaseError(e)));
}
}