title: Confusing Auth domain setting in Firebase
body: <p>There seem to be multiple places to set the auth domain in a Firebase app.</p>
  
  <ol>
  <li><p>Firebase console > Authentication > Sign in methods > Auth domains</p></li>
  <li><p>AuthDomain property of the Firebase config object</p></li>
  <li><p>developers.google.com > Credentials > API Keys > Key restriction</p></li>
  </ol>
  
  <p>In a production app, do we have to set auth domain in all these places? Does the setting of auth domain in these different places actually have different purposes?</p>