httpRefererMatchesBaseUrl()

appcontroller.php

<?php
    private function httpRefererMatchesBaseUrl() {
        if (!array_key_exists('HTTP_REFERER', $_SERVER) ||
           !get_instance()->config->item('base_url')) {
            return false;
        }

        $baseUrl = parse_url(get_instance()->config->item('base_url'));
        $referer = parse_url($_SERVER['HTTP_REFERER']);
        $cleanHttpReferer = $referer['host'];
        $cleanBaseUrl = $baseUrl['host'];

        // Strip the "m." prefix, if it exists
        if (stripos($cleanBaseUrl, 'm.') === 0) {
            $cleanBaseUrl = substr($cleanBaseUrl, 2);
        }
        if (stripos($cleanHttpReferer, 'm.') === 0) {
            $cleanHttpReferer = substr($cleanHttpReferer, 2);
        }

        // Strip the lang subdomain, if it exists
        if (stripos($cleanBaseUrl, '.') === 2) {
            $cleanBaseUrl = substr($cleanBaseUrl, 3);
        }
        if (stripos($cleanHttpReferer, '.') === 2) {
            $cleanHttpReferer = substr($cleanHttpReferer, 3);
        }

        return ($cleanHttpReferer === $cleanBaseUrl);
    }
?>