Ensure a web request is coming from github. Useful for setting up web hooks

github_origin.php

<?php

function githubOrigin() {

  function netMatch($CIDR,$IP) {
      list ($net, $mask) = explode ('/', $CIDR);
      return ( ip2long ($IP) & ~((1 << (32 - $mask)) - 1) ) == ip2long ($net);
  }
  return (netMatch("204.232.175.64/27",$_SERVER['REMOTE_ADDR']) || netMatch("192.30.252.0/22",$_SERVER['REMOTE_ADDR']));
}

//Make sure this request has come from a github IP

if (!githubOrigin()) die('Unauthorized');