feat(auth, android): Play Games provider sign-in support

[russellwheatley]

Description

Writing the code is easier than receiving the serverAuthCode for use in signing in with Play Games provider. Some changes required are already in the example app.

Configuration

Requires setting up a game app on the Play console and following the two sections in the Firebase documentation here:

• https://firebase.google.com/docs/auth/android/play-games#set-up-firebase-project
• https://firebase.google.com/docs/auth/android/play-games#configure-play-games-with-firebase-info

Do not to forget to "publish" the app on the Play console. (For Invertase devs, it is on the Play console under "Play Game App").

Play Game SDK setup

I couldn't find any Dart packages that retrieve the serverAuthCode so I setup myself using the Play Games SDK.

I would not follow the Firebase docs as it has a tiny snippet of the deprecated Play Games SDK (v1) here: https://firebase.google.com/docs/auth/android/play-games#integrate_play_games_sign-in_into_your_game

I would follow the Play Games V2 SDK documentation here: https://developers.google.com/games/services/android/signin

I actually tested directly in the FlutterFirebaseAuthPlugin. A couple of required changes are included in this PR for the auth example app, but I had to add a dependency to the firebase_auth plugin build.gradle (not included in PR):

    dependencies {
        api firebaseCoreProject
        implementation platform("com.google.firebase:firebase-bom:${getRootProjectExtOrCoreProperty("FirebaseSDKVersion", firebaseCoreProject)}")
        implementation 'com.google.firebase:firebase-auth'
// THIS LINE
        implementation "com.google.android.gms:play-services-games-v2:19.0.0"
        implementation 'androidx.annotation:annotation:1.7.0'
    }

For implementation, I had to do the following to get the serverAuthCode:

GamesSignInClient gamesSignInClient = PlayGames.getGamesSignInClient(getActivity());  
  
gamesSignInClient  
    .signIn()  
    .addOnCompleteListener(  
        task -> {  
          if (task.isSuccessful()) {  
            gamesSignInClient  
                .requestServerSideAccess(  
                    "406099696497-a12gakvts4epfk5pkio7dphc1anjiggc.apps.googleusercontent.com",  
                    false)  
                .addOnCompleteListener(  
                    tasky -> {  
                      if (tasky.isSuccessful()) {  
						//SERVER AUTH CODE
                        String serverAuthCode = tasky.getResult();  
                      } else {  
                        result.error(  
                            FlutterFirebaseAuthPluginException.parserExceptionToFlutter(  
                                tasky.getException()));  
                      }  
                    });  
          } else {  
            result.error(  
                FlutterFirebaseAuthPluginException.parserExceptionToFlutter(  
                    task.getException()));  
          }  
        });

Also add in instance creation of class:

PlayGamesSdk.initialize(getActivity());

Related Issues

closes #12190

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[Lyokone]

Looks good, I wonder if we should add a section in the docs as well?