title: How to know if user came from a Facebook link?
body: <p>If there is a link posted on Facebook to my website, and a user follows it, I would like to display custom content using PHP. I tried with the following method...</p>
  
  <pre><code>$_SERVER['HTTP_REFERER']
  </code></pre>
  
  <p>Facebook must block this feature because it is not working. Is there a method for this that actually works with Facebook?</p>