Copyright (c) 2017 Google Inc. All rights reserved.

This sample demonstrates how to obtain an OAuth server auth code on an Android device and send it to a backend server application. The backend server then exchanges the auth code for an access token, which can be used to make calls to the Play Game Services Web API on behalf of the authenticated user.

The client is an Android application that uses the Play Game Services API to sign in and interact with the Games API as normal. It requests the OAuth server auth code that is sent to the server.

The server in the sample is a Java application that runs Jetty as the servlet container. This is done for the sample since it is easy to start and run. In practice, you would run the Servlet on a real server or on Google App Engine.

Configuring a game with a backend server requires three steps:

1. Configure the game in the Google Play Developer Console.
2. Follow the instructions for creating a client ID for Android. Be particularly careful when entering your package name and your certificate fingerprints, since mistakes on those screens can be difficult to recover from.
3. Create an associated web app. If you don't know the address of the server when creating credentials for the web app on the console, you can enter a valid URL (localhost is not accepted!). Once the address is known, you can modify the credentials.

1. In Android Studio, click Run/Run... on the menu and select '0 Edit Configurations...'.
2. Click the plus (+) above the list of configurations and select 'Application'.
3. Change the name to 'Server'.
4. Click the selection button next to Main Class and select 'GameServer (com.google.sample.games)'.
5. In the dropdown named "Classpath of Module", select 'ServerApp'.
6. Press 'Run'.

This should start the server app an in the run window in Android Studio. You should see some logging messages, such as Started [email protected]:8765.

To verify that the server is running, retrieve the test player at http://localhost:8765/player/test.

In order for the client application on the device to access the sample server application, the server application needs to be running on a server which has an address that resolvable from the device. You can test this on the device by using the web browser.

Some common ways to set this up are:

• On a public web server.
• A web server that is known to the DNS servers configured by your local wifi.
• IP address that reachable from the device.
• Using a port forwarder application such as Ngrok.

Once you have the address of the running server application. Add it to the credentials of your web app on the Play Console. Once that is done, download the client_secret.json file for your application and replace the sample client_secret.json with yours.

Restart your server application so it will be ready for the client application.

You'll need to configure the external resources for the client app in order to run the sample:

1. In res/values/serverconfig.xml set the webclient_id to the client id of the associated web app configured in the Google Play Developer Console. Also set host_url to the address of the server running the sample backend app.
2. In the Google Play Developer Console, edit the web app credentials and add the host_url value to the list of addresses for the web app.
3. In the Google Play Developer Console, select a game resource (such as Events) and click on 'Get Resources'. Copy the Android resources to the clipboard and paste the resources into res/values/game-ids.xml.
4. Change the applicationId in ClientApp/build.gradle to match the package name configured for the associated Android App in the console.

Once the above steps are done, run the ClientApp on a device.

To validate that everything is working:

1. Make sure the server app is running by starting it and going to <host_url>/player/test.
2. Start the client app, and press 'Sign In'. This will sign in the client to Play Game Services on the device.
3. In the client app, press Post AuthCode to server. This will get an authcode and send it to the server, which will respond with the player object.

Post questions to this Github project.