Server Side Request Forwarder - accepts client side post requests and submits them to the real destination server side

request_forwarder.php

<?php
  // Assuming a POST to this script in form of:
  // request_forwarder?url=url_name
  //
  // This will convert a client side AJAX request to a server side PHP curl,
  // thus eleminating worries of cross-site scripting and having to abide by
  // cross-origin-request-sharing (CORS) settings on the end server.

  $url = $_GET['url'];
  $fields_string = '';

  //url-ify the data for the POST
  foreach($_POST as $key=>$value) {
    $fields_string .= $key . '=' . $value . '&';
  }
  rtrim($fields_string, '&');

  //open connection
  $ch = curl_init();

  //set the url, number of POST vars, POST data
  curl_setopt($ch,CURLOPT_URL, $url);
  curl_setopt($ch,CURLOPT_POST, count($_POST));
  curl_setopt($ch,CURLOPT_POSTFIELDS, $fields_string);

  //execute post
  $result = curl_exec($ch);

  //close connection
  curl_close($ch);
?>

Maybe it would be cool to add some HTTP_X_FORWARDED headers for scripts that require the user's IP-address?