How to know if my page is running in a facebook iframe or not

Question

I'm currently developing a site which runs standalone and as a facebook app on an iframe I was wondering what whold be "best practice" for checking if my page is ran in a facebook iframe before the page loads so I can preset the relevant CSS and other variables

Thanks.

Answer 1

$signed_request = $_POST['signed_request'];

if(empty($signed_request))
      die('No direct access.');