Simple ping test for cross-domain request.

gistfile1.php

<?php

header("Content-Type: application/json");

// Allow Credentials
header('Access-Control-Allow-Credentials: true');

// Allow all origins
if (isset($_SERVER['HTTP_REFERER']) || isset($_SERVER['HTTP_ORIGIN'])) {
  if (isset($_SERVER['HTTP_REFERER'])) {
    $url_components = parse_url($_SERVER['HTTP_REFERER']);
  } else if (isset($_SERVER['HTTP_ORIGIN'])) {
    $url_components = parse_url($_SERVER['HTTP_ORIGIN']);
  }
  if (isset($url_components['port'])) {
    header('Access-Control-Allow-Origin: ' . $url_components['scheme'] . '://' . $url_components['host'] . ':' . $url_components['port']);
  } else {
    header('Access-Control-Allow-Origin: ' . $url_components['scheme'] . '://' . $url_components['host']);
  }
} else {
  header('Access-Control-Allow-Origin: *');
}

// Specify which request methods are allowed
header('Access-Control-Allow-Methods: GET, POST, DELETE, OPTIONS');

// Additional headers which may be sent along with the CORS request
// The X-Requested-With header allows jQuery requests to go through
//header('Access-Control-Allow-Headers: X-Requested-With');
header('Access-Control-Allow-Headers: Origin, X-Requested-With, Content-Type, Accept');

//// Exit early so the page isn't fully loaded for options requests
//if (strtolower($_SERVER['REQUEST_METHOD']) == 'options') {
//  exit();
//}

echo json_encode(array("Message" => "OK!"));
?>