public function isValid(SignatureComposer $composer)
    {
        // Constant Time String Comparison @see http://php.net/hash_equals
        if (!function_exists('hash_equals')) {
            // Polyfill for PHP < 5.6
            return Security::hashEquals($composer->compose($this->parameters), $this->signature);
        } else {
            return hash_equals($composer->compose($this->parameters), $this->signature);
        }
    }