title: how to use facebook for user login on my website?
body: <p>i am wondering how facebook works for logging in user on our websites.</p>
  
  <p>I mean a user needs to be registered to my website for posting a comment, how can I check trough my php code if it's a logged user?</p>
  
  <p>I heard you can only check if it's a logged user with javascript</p>
  
  <p>Thanks for any explanation</p>