Google+ authentication android

Hi!

I want my users to be able to login using their google account every time at app startup, until user decides to logout. I managed to do that using tokens:

         // Set login info.
 
         service = new SpreadsheetsService("app-name");
 
         
 
         // Create OAuth2 Parameters.
 
         oAuthParams = new OAuth2Parameters();
 
         oAuthParams.ClientId = CLIENT_ID;
 
         oAuthParams.ClientSecret = CLIENT_SECRET;
 
         oAuthParams.RedirectUri = REDIRECT_URI;
 
         oAuthParams.Scope = SCOPE;

     public void Authenticate()
 
     {       
 
         // Open web browser for user to authenticate.
 
         string authUrl = OAuthUtil.CreateOAuth2AuthorizationUrl(oAuthParams);
 
         Application.OpenURL(authUrl);
 
     }

     public bool FinishAuthenticate(string accessCode)
 
     {
 
         // Save access code.
 
         oAuthParams.AccessCode = accessCode;
 
  
 
         try
 
         {
 
             // Get access token.
 
             OAuthUtil.GetAccessToken(oAuthParams);
 
             myToken = oAuthParams.AccessToken;
 
             PlayerPrefs.SetString ("myToken", myToken);
 
             mySecretToken = oAuthParams.ClientSecret;
 
             PlayerPrefs.SetString ("mySecretToken", mySecretToken);
 
             myRefreshToken = oAuthParams.RefreshToken;
 
             PlayerPrefs.SetString ("myRefreshToken", myRefreshToken);
 
  
 
             // Save data to make authorized requests.
 
             GOAuth2RequestFactory requestFactory = new GOAuth2RequestFactory(null, "app-name", oAuthParams);
 
             service.RequestFactory = requestFactory;
 
  
 
             myUserName = GetUserName ();
 
             logged = true;
 
             return true;
 
         }
 
         catch (WebException)
 
         {
 
             return false;
 
         }
 
     }

and that works perfect in standalone, but I want to use the phone's google accounts on android, so the user will not be redirected to the web browser and copy the key.

Is that possible in unity? I searched a while but could not find a proper solution for this.