how do I detect if user logined using my login button or login from facebook?

Hi,
I implemented my facebook log in to my website but how do I know if the user used my log in button OR the user logged in by going to facebook.com.
This way I can detect and take some action if he or she did not use my facebook log in button I used javascript API
Other than that, every thing is working. but this is a big issue for me right now
Thanks for any help or advice in advance

Unless a Facebook API is giving you the login referrer, there would be no way to find that out.