我在flutter web framework中集成google sign in web包时遇到了问题。我想找回idToken，但我做不到。

final GoogleSignIn _googleSignIn = GoogleSignIn(
    clientId:  'my client id'
    signInOption: SignInOption.standard,
    scopes: [
      'email',
    ],
  );
     _googleSignIn.onCurrentUserChanged
            .listen((GoogleSignInAccount? account) async {
    
          // In mobile, being authenticated means being authorized...
          bool isAuthorized = account != null;
          debugPrint('silentUserLogin account is : $account');
          // However, in the web...
          if (kIsWeb && account != null) {
            isAuthorized = await _googleSignIn.canAccessScopes(scopes);
          }
    
    
          // Now that we know that the user can access the required scopes, the app
          // can call the REST API.
        });

在widget中，我这样做了

/// Renders a web-only SIGN IN button.
Widget buildSignInButton({HandleSignInFn? onPressed}) {
  return (GoogleSignInPlatform.instance as web.GoogleSignInPlugin)
      .renderButton();
}

我收到了这个

GoogleSignInAccount:{displayName: Brahim CHEBBI, email: [email protected], id: 113873915042996649214, photoUrl: https://lh3.googleusercontent.com/a/AAcHTtdesTEaIgpxbI0e3jxNnPwkwEe6K_ylHIAea7uDdBfnIg=s96-c, serverAuthCode: null}

我不明白为什么serverAuthCode为null，我想知道如何检索idToken。