title: Show 404 error page from PHP file, without redirecting
body: <p>I have a file <code>secret.php</code> which is included in <code>index.php</code> and I want to show a 404 error page when someone tries to access <code>secret.php</code> directly. But</p>
  
  <pre><code>header("Location: this_site_certainly_does_not_exist");
  </code></pre>
  
  <p>in <code>secure.php</code> is not a solution, because I want the URL the user typed (e.g. <code>example.com/secret.php</code>) to be visible in the browser's URL bar when the error page is shown, instead of redirecting.</p>