Checks if request is a AJAX-Request

onlyForAjax.php

<?php 

$ajax = false;

if(!empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) === 'xmlhttprequest') 
{
    $ajax = true;
}

if (!$ajax) 
{
    header("HTTP/1.0 401 Not AJAX");

    echo "<h1>HTTP Status : 401 - Access is denied!</h1>
          <h3>Message: You have no permission to access this page</h3>";
    die();
}