I'm trying to detect the x-forwarded-for header for users of the Puffin browser on my website. If I connect to here using Puffin it detects my real ip even though Puffin uses a proxy (it renders on its cloud servers). I tried another test site and that identified the x-forwarded-for header which had my real ip in it.
However, using a php script on my own server to try and detect x-forwarded-for as follows:
$ip = $_SERVER['X-FORWARDED-FOR'];
it doesn't work. I've tried numerous other ways to detect it but none of them work. Any ideas what I might be doing wrong or how I should detect this particular header?