google_sign_in Flutter 插件总是返回 null serverAccessCode

Question

I have the current workflow for my authentication

1. User signs in via google OAuth2
2. User is then given a server_auth_code which they send to my backend authentication
3. The auth code is validated on the back end and users is sent a JWT

I had this all working in raw Java with the Android SDK, but Flutter seemed a lot nicer. But now when using the google_sign_in plugin on android, I am unable to retrieve the serverAuthCore anymore, this plugin just wants to return null the entire time.

I Am using the client ID that's specified for Android, however, I tested the WebApplication that's auto-generated by google too but that's the same issue (Null serverAutHCode)

This is the code that I am currently using:

/// Provides the `GoogleSignIn` class
import 'package:google_sign_in/google_sign_in.dart';

class GoogleLoginPage extends StatefulWidget {

  final String name = "Logging in with google.";

  late GoogleSignIn _googleSignIn;

  GoogleLoginPage() : super() {
    _googleSignIn = GoogleSignIn(
        scopes: ['https://www.googleapis.com/auth/userinfo.email',
        'https://www.googleapis.com/auth/userinfo.profile'],
        serverClientId: "XX-XXX.apps.googleusercontent.com"
    );
  }

  Future<void> fetchAuthToken() async {
    try {
      var response = await _googleSignIn.signIn();
      log(response?.serverAuthCode ?? "No server auth code");
      _googleSignIn.signOut();
    } catch (error) {
      print("ERR");
      print(error);
    }
  }

  @override
  State<GoogleLoginPage> createState() => GoogleLoginState();

}

The output of this code is: [log] No server auth code

The question:

Am I doing something wrong? As mentioned this works 100% on my java project using the google play services SDK so I know it's nothing to do with my google console configurations.

Answer 1

Okay so I figured out the issues:

It appears that by default the google login plugin for flutter comes on an older version (If I remember correctly it was 20.0.5)

I Simply changed the version to the latest version:

'com.google.android.gms:play-services-auth:20.2.0'

You can do this by editing the project's build.gradle (In IntelliJ you open build.gradle and click "Open for editing in the android studio" in the top right, from there you need to find the gradle file for google_sign_in, and change the import there, remember to click sync in the top right of android studio before you close out of it)

And I began to receive my serverAuthCode as normal, cheers!