title: Social.localUser.Authenticate returns false everytime in Unity
body: <p>I am using the latest version of GooglePlayGames plugin ( 0.9.50). I have added the  Android resouces from play console. I have also verified that my SHA-1 fingerprint is correct. The SHA-1 fingerprint of upload certificate in Google play console and the OAuth 2.0 client ID in Google developer console are same. Still Social.localUser.Authenticate returns false everytime. I have also tried publishing my game in alpha after adding the tester's accounts. Still Social.localUser.Authenticate returned false. When I open the game from my phone, not even that Google Play Games Sign-in "green thing" is showing. I don't have any errors or warnings. The following is my code:</p>
  
  <pre><code>using GooglePlayGames;
  using GooglePlayGames.BasicApi;
  using UnityEngine;
  using UnityEngine.SocialPlatforms;
  using GooglePlayGames;
  
  public class Playgames : MonoBehaviour {
  
  public bool IsConnectedToGoogleServices { set; get; }
  
  // Use this for initialization
  void Start () {
      #if (UNITY_ANDROID || (UNITY_IPHONE &amp;&amp; !NO_GPGS))
      PlayGamesClientConfiguration config = new PlayGamesClientConfiguration.Builder().Build();
      PlayGamesPlatform.InitializeInstance(config);
      PlayGamesPlatform.DebugLogEnabled = true;
      PlayGamesPlatform.Activate();
      #endif
  
      SignIn();
  }
  
  public bool SignIn()
  {
      if (!IsConnectedToGoogleServices) {
          Social.localUser.Authenticate ((bool success) =&gt; {
              IsConnectedToGoogleServices = success;
              Debug.Log("Sign-in " + success.ToString() );
          });
      }
      return IsConnectedToGoogleServices;
  }
  }
  </code></pre>
  
  <p>Could someone please help me fix this? Thanks in advance.</p>