src/HTTP/Request2/Adapter/Socket.php
protected function createDigestResponse($user, $password, $url, &$challenge)
    {
        if (false !== ($q = strpos($url, '?'))
            && $this->request->getConfig('digest_compat_ie')
        ) {
            $url = substr($url, 0, $q);
        }

        $a1 = md5($user . ':' . $challenge['realm'] . ':' . $password);
        $a2 = md5($this->request->getMethod() . ':' . $url);

        if (empty($challenge['qop'])) {
            $digest = md5($a1 . ':' . $challenge['nonce'] . ':' . $a2);
        } else {
            $challenge['cnonce'] = 'Req2.' . rand();
            if (empty($challenge['nc'])) {
                $challenge['nc'] = 1;
            }
            $nc     = sprintf('%08x', $challenge['nc']++);
            $digest = md5(
                $a1 . ':' . $challenge['nonce'] . ':' . $nc . ':' .
                $challenge['cnonce'] . ':auth:' . $a2
            );
        }
        return 'Digest username="' . str_replace(array('\\', '"'), array('\\\\', '\\"'), $user) . '", ' .
               'realm="' . $challenge['realm'] . '", ' .
               'nonce="' . $challenge['nonce'] . '", ' .
               'uri="' . $url . '", ' .
               'response="' . $digest . '"' .
               (!empty($challenge['opaque'])?
                ', opaque="' . $challenge['opaque'] . '"':
                '') .
               (!empty($challenge['qop'])?
                ', qop="auth", nc=' . $nc . ', cnonce="' . $challenge['cnonce'] . '"':
                '');
    }
protected function createDigestResponse($user, $password, $url, &$challenge)
    {
        if (false !== ($q = strpos($url, '?'))
            && $this->request->getConfig('digest_compat_ie')
        ) {
            $url = substr($url, 0, $q);
        }

        $a1 = md5($user . ':' . $challenge['realm'] . ':' . $password);
        $a2 = md5($this->request->getMethod() . ':' . $url);

        if (empty($challenge['qop'])) {
            $digest = md5($a1 . ':' . $challenge['nonce'] . ':' . $a2);
        } else {
            $challenge['cnonce'] = 'Req2.' . rand();
            if (empty($challenge['nc'])) {
                $challenge['nc'] = 1;
            }
            $nc     = sprintf('%08x', $challenge['nc']++);
            $digest = md5(
                $a1 . ':' . $challenge['nonce'] . ':' . $nc . ':' .
                $challenge['cnonce'] . ':auth:' . $a2
            );
        }
        return 'Digest username="' . str_replace(array('\\', '"'), array('\\\\', '\\"'), $user) . '", ' .
               'realm="' . $challenge['realm'] . '", ' .
               'nonce="' . $challenge['nonce'] . '", ' .
               'uri="' . $url . '", ' .
               'response="' . $digest . '"' .
               (!empty($challenge['opaque'])?
                ', opaque="' . $challenge['opaque'] . '"':
                '') .
               (!empty($challenge['qop'])?
                ', qop="auth", nc=' . $nc . ', cnonce="' . $challenge['cnonce'] . '"':
                '');
    }
Creates a value for [Proxy-]Authorization header when using digest authentication

@param string $user       user name
@param string $password   password
@param string $url        request URL
@param array  &$challenge digest challenge parameters

@return   string  value of [Proxy-]Authorization request header
@link     http://tools.ietf.org/html/rfc2617#section-3.2.2