title: Get username in Firebase authData
body: <p>I'm using Firebase in a node.js backend for authentication.<br>
  After authentication, the data retrieved by Firebase are like this :  </p>
  
  <pre><code>{
    auth: {
      provider: 'password',
      uid: '1234'
    },
    expires: 1452072779,
    token:'token',
    uid: '4567',
    provider: 'password'
  }
  </code></pre>
  
  <p>However I cannot get the <strong>username</strong>. Do you know if there is a way to get it ?</p>