OAuthData ProcessLogin method

Hello community,

I have a somes questions about this method, I know this method is called when the user is redirected to Telligent Evolution after logging in through the OAuth service. I also know that should return information provided by the service or return null. Now:

  1. what happens internally when you return null?
  2. What is going to see the end user if we return null? 
  3. If we return null, because a validation or a failed login or whatever, is there anything else we need to add in the login widget?

Thanks in advance!