protected function backURLToken(HTTPRequest $request)
    {
        $backURL = $request->getVar('BackURL');
        if (!strstr($backURL, '?')) {
            return null;
        }

        // Filter backURL if it contains the given request parameter
        list(,$query) = explode('?', $backURL);
        parse_str($query, $queryArgs);
        $name = $this->getName();
        if (isset($queryArgs[$name])) {
            return $queryArgs[$name];
        }
        return null;
    }