title: Get domain of a POST request
body: <p>I have a script that makes a <strong><em>POST</em></strong> request to my website from other websites (different domains) and I need to know if it's possible to get what's that other domain.</p>
  
  <p>Like: <strong>helloworld.com</strong> uses my script and it executes a <strong><em>POST</em></strong> request with <strong>mywebsite.com</strong>. How does <strong>mywebsite.com</strong> know that the request is from <strong>helloworld.com</strong>?</p>
  
  <p>I have tried with <code>$_SERVER['REMOTE_HOST']</code> but that's not working.</p>