protected function shouldUseServerDigestAuth(HTTP_Request2_Response $response)
    {
        // no sense repeating a request if we don't have credentials
        if (401 != $response->getStatus() || !$this->request->getAuth()) {
            return false;
        }
        if (!$challenge = $this->parseDigestChallenge($response->getHeader('www-authenticate'))) {
            return false;
        }

        $url    = $this->request->getUrl();
        $scheme = $url->getScheme();
        $host   = $scheme . '://' . $url->getHost();
        if ($port = $url->getPort()) {
            if ((0 == strcasecmp($scheme, 'http') && 80 != $port)
                || (0 == strcasecmp($scheme, 'https') && 443 != $port)
            ) {
                $host .= ':' . $port;
            }
        }

        if (!empty($challenge['domain'])) {
            $prefixes = array();
            foreach (preg_split('/\\s+/', $challenge['domain']) as $prefix) {
                // don't bother with different servers
                if ('/' == substr($prefix, 0, 1)) {
                    $prefixes[] = $host . $prefix;
                }
            }
        }
        if (empty($prefixes)) {
            $prefixes = array($host . '/');
        }

        $ret = true;
        foreach ($prefixes as $prefix) {
            if (!empty(self::$challenges[$prefix])
                && (empty($challenge['stale']) || strcasecmp('true', $challenge['stale']))
            ) {
                // probably credentials are invalid
                $ret = false;
            }
            self::$challenges[$prefix] =& $challenge;
        }
        return $ret;
    }