static function _httpResponseToMessage($response)
    {
        // Should this function be named Message.fromHTTPResponse instead?
        $response_message = Auth_OpenID_Message::fromKVForm($response->body);

        if ($response->status == 400) {
            return Auth_OpenID_ServerErrorContainer::fromMessage(
                        $response_message);
        } else if ($response->status != 200 and $response->status != 206) {
            return null;
        }

        return $response_message;
    }