public function toArray()
    {
        $array = array();
        $allowed = get_class_vars(get_class($this));
        foreach (get_object_vars($this) as $key => $item) {
            if (array_key_exists($key, $allowed) && isset($item)) {
                $array[constant(strtoupper("CURLOPT_" . $key))] = (method_exists($item, 'build') ? $item->build() : $item);
            }
        }
        return $array;
    }