title: Grails spring security core, how to set principal manually
body: <p>Hi im trying to make facebook's login in a grails app, the problem I have is that when the user is logged in facebook, spring security core doesn't recognize him, how can I set the user's principal manually?
  I can look for the user object but i don't know how to set it in order to get a true user when i call getAuthenticatedUser() (now it returns a null object)</p>
  
  <p>Thanks in advance,
  Regards</p>