title: Google Identity Signin API always returns NULL with Server Client ID
body: <p><strong>[Addition]</strong> </p>
  
  <p>Based on my observations since having this issue: I feel like the issue is either dealing with...</p>
  
  <ul>
  <li>A bad Server Client ID</li>
  <li>Additional programming needed that is not provided out-of-the-box (i.e. an app engine module or server)</li>
  </ul>
  
  <hr>
  
  <p><strong>[Original]</strong></p>
  
  <p>I have successfully ran the sample at <a href="https://github.com/googlesamples/google-services/tree/master/android/signin/app" rel="nofollow noreferrer">Google Sign-In Android Sample App</a>. 
  My issue deals with the 2 Activities...ServerAuthCodeActivity and IdTokenActivity. </p>
  
  <p>I went through the process of creating the <code>google-services.json</code> file and placed it in the correct spot. When I ran the app, I was able to successfully use 2 of the 4 provided Activities...</p>
  
  <ul>
  <li>Sign-in Activity: Basic Signing in</li>
  <li>Sign-in with Drive Activity: Basic Signing in plus Drive Authentication</li>
  <li><strong>ID Token Activity: Retrieves the ID Token form the logged in user</strong></li>
  <li><strong>Server Authentication Code Activity: Retrieve an Authentication code from an authenticated server.</strong></li>
  </ul>
  
  <p>The first 2 examples work very well; <strong>however, the last 2 activities just give me a</strong> <code>null</code> <strong>result.</strong></p>
  
  <p>Before I could run the app, I noticed I needed to provide a <code>server_client_id</code> in <code>strings.xml</code>. I seen that the <code>google-services.json</code> had an OAuth client id that matched the requirements (ending in <code>apps.googleusercontent.com</code>), and placed that client id in the <code>strings.xml</code> file. Note: I tried to create an Android OAuth Client ID in the <code>Google Developer Console</code>, but it stated that I already had an OAuth Client ID for that project / package. So I figured the <code>google-services.json</code> file's client id was correct.</p>
  
  <p><strong>So, is that the correct Server Client ID? Or am I suppose to get that ID from somewhere else?</strong></p>
  
  <p><strong>Edit</strong></p>
  
  <p>Here is my <code>google-services.json</code> file (condensed)</p>
  
  <pre><code>{
  
   "project_info": {
    ...
   },
   "client": [
     {
       "client_info": {
         ...
       },
       "oauth_client": [
         {
           "client_id": "*****.apps.googleusercontent.com", // HERE
           ...
         }
       ],
       ...
     }
   ],
   ...
  }
  </code></pre>
  
  <p>Here is the result of the Authentication code after signing in
  <img src="https://i.stack.imgur.com/A7ZSx.jpg" width="400" height="680"></p>