如何在flutter中获取google登录访问令牌

dependencies:
  google_sign_in: ^5.0.0

import 'package:google_sign_in/google_sign_in.dart';

GoogleSignIn _googleSignIn = GoogleSignIn(
  scopes: [
    'email',
    'https://www.googleapis.com/auth/contacts.readonly',
  ],
);

GoogleSignInAccount? _currentUser;

Future<void> _handleSignIn() async {
  try {
    await _googleSignIn.signIn();
    setState(() {
      _currentUser = _googleSignIn.currentUser;
    });
  } catch (error) {
    print('Google Sign-In error: $error');
  }
}

String? _accessToken;

void _getAccessToken() async {
  if (_currentUser != null) {
    String? accessToken = await _currentUser!.authHeaders['Authorization'];
    setState(() {
      _accessToken = accessToken;
    });
  }
}