title: Chat App with Firebase
body: <p>I am learning Firebase Cloud Messaging and I am trying to build a sample chat app.
  I could successfully integrate with Firebase and I add messages to Realtime database. </p>
  
  <p>Now to do One to One Chat,</p>
  
  <ol>
  <li>Do I need to use Firebase provided Authentication mechanism to add new users?</li>
  <li>If yes I already have a custom users table, Is there a way to integrate these users with firebase?</li>
  </ol>