auth_service.dart

import 'package:apple_sign_in/apple_sign_in.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/services.dart';

class AuthService {
  final FirebaseAuth _firebaseAuth = FirebaseAuth.instance;

  Future<FirebaseUser> signInWithApple() async {
    final result = await AppleSignIn.performRequests([
      AppleIdRequest(requestedScopes: [Scope.fullName, Scope.email])
    ]);

    switch (result.status) {
      case AuthorizationStatus.authorized:
        {
          final appleIdCredential = result.credential;

          final AuthCredential credential =
              OAuthProvider(providerId: 'apple.com').getCredential(
            accessToken:
                String.fromCharCodes(appleIdCredential.authorizationCode),
            idToken: String.fromCharCodes(appleIdCredential.identityToken),
          );

          final firebaseUser =
              (await _firebaseAuth.signInWithCredential(credential)).user;

          return firebaseUser;
        }

      case AuthorizationStatus.error:
        {
          throw PlatformException(
            code: 'ERROR_AUTHORIZATION_DENIED',
            message: result.error.toString(),
          );
        }

      case AuthorizationStatus.cancelled:
        throw PlatformException(
          code: 'ERROR_ABORTED_BY_USER',
          message: 'Sign in aborted by user',
        );
    }

    return null;
  }
}