title: Firebase Auth, how to know new user signed up, rather than existing user sign in?
body: <p>My use case is that I want to ask newly signed up users to enrich basic info like their names.
  So I was hoping to do it like:</p>
  
  <pre><code>firebase.auth().onAuthStateChanged(function(user) {
    if (user) {
      // User is signed in.
      if (some indicator tells me it is newly signed up user)
          {redirect to a form to fill in more info}
    } else {
      // No user is signed in.
    }
  });
  </code></pre>
  
  <p>I checked the doc, and could not find anything related to this...</p>
  
  <p>Thanks for the help in advance.</p>