title: Firebase - What this means to set custom parameters to provider?
body: <p>Currently i am working with firebase authentication. And found many of tutorials, they set custom parameters to provider like that</p>
  
  <pre><code>const provider = new firebase.auth.GoogleAuthProvider();
  provider.setCustomParameters({ prompt: 'select_account' });
  </code></pre>
  
  <p>What this actually means setting custom parameters <code>prompt</code> ? Why we need to set custom parameters like that - in this case <code>prompt: 'select_account'</code> ?</p>