title: How to validate Email address using Firebase
body: <p>I'm doing a two step sign up process. First email, then password.</p>
  
  <p>I'd like to validate if the email is not in use or badly formatted first. If it's ok, then show the password form.</p>
  
  <p>Right now I can't find a good way to verify if the email is used.</p>
  
  <p>I'd expect something like this:</p>
  
  <pre><code> firebaseAuth.validateEmailAddress(email)
  </code></pre>