protected function validateAndSanitizeSignedProtocol($signedProtocol)
    {
        Validate::canCastAsString($signedProtocol, 'signedProtocol');
        // sanitize string
        $sanitizedSignedProtocol = strtolower($signedProtocol);
        if (strlen($sanitizedSignedProtocol) > 0) {
            if (strcmp($sanitizedSignedProtocol, "https") != 0 && strcmp($sanitizedSignedProtocol, "https,http") != 0) {
                throw new \InvalidArgumentException(Resources::SIGNED_PROTOCOL_INVALID_VALIDATION_MSG);
            }
        }

        return $sanitizedSignedProtocol;
    }