title: Firebase disable automatic login account creation
body: <p>I am building a web and mobile app using firebase. When signing with Google, firebase auto creates a new account in the project (Auth) if one does not exist. Its fine with the mobile app. </p>
  
  <p>But with the web, I just want existing users (who created accounts with mobile app) to signin and not create new accounts via web.</p>
  
  <p>How do I setup firebase not to create new accounts if one does not exist?</p>