code: public void loginWithGoogle(final String accessToken, final SimpleLoginAuthenticatedHandler completionHandler) {
          if(accessToken == null) {
              handleInvalidInvalidToken(completionHandler);
          }
          else {
              HashMap<String, String> data = new HashMap<String, String>();
              data.put("access_token", accessToken);
  
              loginWithToken(Constants.FIREBASE_AUTH_GOOGLE_PATH, Provider.GOOGLE, data, completionHandler);
          }
      }
docs: Login to Firebase using a Google access token. The returned FirebaseSimpleLoginUser object will contain pertinent
  Google data accessible with getThirdPartyUserData().
  
  @param accessToken Access token returned by Facebook SDK.
  @param completionHandler Handler for asynchronous events.