title: Firebase Cloud Messaging: best practice
body: <p>I'm migrating to Firebase Cloud Messaging, and I have one doubt.
  My application must show the login screen when launching, and if the user performs login in another account, I must stop send notifications for the older user.</p>
  
  <ul>
  <li>What's the best way to do that?</li>
  <li>Can I force the application to renew the token?</li>
  <li>Or should I update the token's owner in my base by my own?</li>
  </ul>