title: Check if an email already exists in Firebase Auth in Flutter App
body: <p>I'm currently developing a flutter app that requires users to register before using it. I use Firebase Authentication and would like to check whether an email is already registered in the app. </p>
  
  <p>I know the easy way to do it is to catch the exception when using the <code>createUserWithEmailAndPassword()</code> method (as answered in <a href="https://stackoverflow.com/questions/51387031/find-whether-email-and-username-already-exist-in-firebase-auth-in-flutter-app">this question</a>). The problem is that I ask for the email address in a different route from where the user is registered, so waiting until this method is called is not a good option for me. </p>
  
  <p>I think the best option would be to use the method <code>fetchProvidersForEmail()</code>, but I can't seem to make it work. </p>
  
  <p>How do I use that method? Or is there a better option to know if an email is already registered?</p>