title: Firebase Cloud Messaging - How to validate Tokens?
body: <p>I am using Firebase Cloud Messaging (FCM) and as per the abreviated code below everytime a new Token is generated on the Customer Device... I send this new TOKEN to my SERVER DB (Cloud) where I save it in order to be able to send future <strong>Push Notification</strong> from the Server to the Device using the CFM API.</p>
  
  <pre><code>    //public class CFMInstanceIDService extends FirebaseInstanceIdService ...
  
      public void onTokenRefresh() {
          ...
          String cfmToken = FirebaseInstanceId.getInstance().getToken();        
          ...     
          sendRegistrationToServer(customerGuid, cfmToken);
      }
  </code></pre>
  
  <p>By doing this I have on the Server a list of ALL (multiples) Devices where a Customer is logged-in. (Tablet, Phone, iPhone, Android, etc) </p>
  
  <p><strong>Is there any way to verify/validate a Token at any time?</strong> </p>
  
  <p>I would like to know/ensure that all the tokens that I have associated to a Customer belong to real Devices. I don't want to send Push Notifications to not-existing Tokens.</p>