title: Google oAuth login - How to allow only whitelisted emails to log into my app
body: <p>I'm creating a web app and decided to use google authentication for its ease of use.
  Thing is, I want to only let certain emails login. All other emails should not be able to login!</p>
  
  <p>How do I do that?</p>
  
  <p>I'm aware that I can send the auth token to the backend, verify it with google's library, and then filter the emails but... there should be an easier way, I hope?</p>