title: Parse.com Is it possible to login using facebook while checking if the facebook user's email exists in a user in parse and if it does linking both?
body: <p>I'm having the following problem with the parse iOS SDK. In my app users can login using email (username)/password or facebook. When they use facebook the email (username) gets set automatically. But if the user logs in using email/password first and after logging out tries to login using facebook they get a duplicate account. My goal in this scenario is to link facebook to the previous account. Is there a way to check if the potential new user's email exist in parse database before creating a new account and if it exists then link both account? This way the user doesn't have to remember if they used facebook or email, they could use both seamlessly.</p>
  
  <p>thanks.</p>