in src/Signature/SignatureV2.php [55:66]
    private function getCanonicalizedParameterString(array $params)
    {
        unset($params['Signature']);
        uksort($params, 'strcmp');
        $str = '';
        foreach ($params as $key => $val) {
            $str .= rawurlencode($key) . '=' . rawurlencode($val) . '&';
        }
        return substr($str, 0, -1);
    }