Authenticate in Unity Using Google Play Games Services

You can use Google Play Games services to sign in players to an Android game built on Firebase and Unity. To use Google Play Games services sign-in with Firebase, first sign in the player with Google Play Games, and request an OAuth 2.0 auth code when you do so. Then, pass the auth code to PlayGamesAuthProvider to generate a Firebase credential, which you can use to authenticate with Firebase.

Before you begin

Set up your Unity project

Add the Firebase config file and the Firebase Unity SDK to your Unity project as described in Add Firebase to your Unity project. Follow the instructions for Android.

Be sure to import FirebaseAuth.unitypackage.
In the Unity Editor, under Build Settings > Player Settings > Other Settings set the Android package name of your game.
Then, under Build Settings > Player Settings > Publishing Settings, select or create a keystore and key, which will be used to sign your Android package. Your APK must be signed for Play Games sign-in to work—this requirement applies not just for publishing, but also during development of your game.

Set up your Firebase project

In the Firebase console, go to the Firebase project in which you registered your Unity project.
Set your game's SHA-1 fingerprint from the Settings page of the Firebase console, using the key you set in Unity.

You can get the SHA-1 fingerprint of your key with the keytool command:
```
keytool -exportcert -list -v \
    -alias YOUR-KEY-NAME -keystore PATH-TO-KEYSTORE
```
Alternatively, you can get the SHA hash of your signing certificate with the gradle signingReport command:
```
gradlew signingReport
```
Your APK must be signed with this key, including during development.
Enable Google Play Games as a sign-in provider:
1. In the Firebase console, open the Authentication section.
2. Generate and obtain your project's web server client ID and client secret:
  1. Within the Sign in method tab, enable the Google sign-in provider.
  2. Copy the web server client ID and secret from the Google sign-in provider.
3. Within the Sign in method tab, enable the Play Games sign-in provider, and specify your project's web server client ID and client secret, which you got in the last step.

Configure Play Games services with your Firebase app information

In the Google Play Console, open your Google Play app or create one.
In the Grow section, click Play Games services > Setup & Management > Configuration.
Click Yes, my game already uses Google APIs, select your Firebase project from the list, and then click Use.
On the Play Games services configuration page, click Add Credential.
1. Select the Game server type.
2. In the OAuth client field, select your project's web client ID. Be sure this is the same client ID you specified when you enabled Play Games sign-in.
3. Save your changes.
Still on the Play Games services configuration page, click Add Credential again.
1. Select the Android type.
2. In the OAuth client field, select your project's Android client ID. (If you don't see your Android client ID, be sure you set your game's SHA-1 fingerprint in the Firebase console.)
3. Save your changes.

On the Events, Achievements, and Leaderboards pages, create any Play Games resources you want to use with your game (if you don't want to use any immediately, you can create a placeholder entry). Then, on any of the Events, Achievements, or Leaderboards pages, click Get resources and copy the Android resources snippet somewhere convenient. You will need the snippet to set up the Google Play Games services plugin.

The resources snippet looks like the following example:

<?xml version="1.0" encoding="utf-8"?>
<!--
Google Play game services IDs.
Save this file as res/values/games-ids.xml in your project.
-->
<resources>
  <!-- app_id -->
  <string name="app_id" translatable="false">123456789000</string>
  <!-- package_name -->
  <string name="package_name" translatable="false">com.example.game</string>
  <!-- event Wiped Raid -->
  <string name="event_wiped_raid" translatable="false">CgkIpKjv1a4PEAIYBA</string>
</resources>

On the Testers page, add the email addresses of any users who need to be able to sign in to your game before you release it on the Play Store.

Integrate Play Games sign-in into your game

Download the latest release of the Play Games plugin for Unity and extract it.
Import the plugin's Unity package into your Unity project. You can find the Unity package in the current-build directory of the release archive.
Set up the Play Games plugin:
1. Click Window > Google Play Games > Setup > Android Setup to open the Android Configuration screen.
2. Paste the Android resources snippet you got from the Play console into the Resources Definition field.
3. Paste your web server client ID, which you provided when you enabled Play Games sign-in in the Firebase console, into the Client ID field.
4. Click Setup.

In your game, configure a Play Games client with the RequestServerAuthCode setting enabled:

using GooglePlayGames;
using GooglePlayGames.BasicApi;
using UnityEngine.SocialPlatforms;
using System.Threading.Tasks;

PlayGamesClientConfiguration config = new PlayGamesClientConfiguration.Builder()
    .RequestServerAuthCode(false /* Don't force refresh */)
    .Build();

PlayGamesPlatform.InitializeInstance(config);
PlayGamesPlatform.Activate();

Then, when a player chooses to sign in with Play Games, call Social.localUser.Authenticate():

Social.localUser.Authenticate((bool success) => {
  // handle success or failure
});

Authenticate with Firebase

After you add Play Games sign-in to your game, you can use the auth code from Play Games services to authenticate with Firebase.

After the player has successfully signed in using Play Games, in the sign-in continuation handler, get an auth code for the player's account:

Social.localUser.Authenticate((bool success) => {
  if (success) {
    authCode = PlayGamesPlatform.Instance.GetServerAuthCode();
  }
});

Then, exchange the auth code from Play Games services for a Firebase credential, and use the Firebase credential to authenticate the player:

Firebase.Auth.FirebaseAuth auth = Firebase.Auth.FirebaseAuth.DefaultInstance;
Firebase.Auth.Credential credential =
    Firebase.Auth.PlayGamesAuthProvider.GetCredential(authCode);
auth.SignInAndRetrieveDataWithCredentialAsync(credential).ContinueWith(task => {
  if (task.IsCanceled) {
    Debug.LogError("SignInAndRetrieveDataWithCredentialAsync was canceled.");
    return;
  }
  if (task.IsFaulted) {
    Debug.LogError("SignInAndRetrieveDataWithCredentialAsync encountered an error: " + task.Exception);
    return;
  }

  Firebase.Auth.AuthResult result = task.Result;
  Debug.LogFormat("User signed in successfully: {0} ({1})",
      result.User.DisplayName, result.User.UserId);
});

Next steps

After a user signs in for the first time, a new user account is created and linked to their Play Games ID. This new account is stored as part of your Firebase project, and can be used to identify a user across every app in your project.

In your game, you can get the user's Firebase UID from the Firebase.Auth.FirebaseUser object:

Firebase.Auth.FirebaseUser user = auth.CurrentUser;
if (user != null && user.IsValid()) {
  string playerName = user.DisplayName;

  // The user's Id, unique to the Firebase project.
  // Do NOT use this value to authenticate with your backend server, if you
  // have one; use User.TokenAsync() instead.
  string uid = user.UserId;
}

In your Firebase Realtime Database and Cloud Storage Security Rules, you can get the signed-in user's unique user ID from the auth variable, and use it to control what data a user can access.

To get a user's Play Games player information or to access Play Games services, use the APIs provided by the Play Games plugin.

To sign out a user, call SignOut():

auth.SignOut();