PayWithAmazon\Client::calculateSignatureAndParametersToString PHP Method

    private function calculateSignatureAndParametersToString($parameters = array())
    {
        $parameters['AWSAccessKeyId'] = $this->config['access_key'];
        $parameters['Version'] = self::SERVICE_VERSION;
        $parameters['SignatureMethod'] = 'HmacSHA256';
        $parameters['SignatureVersion'] = 2;
        $parameters['Timestamp'] = $this->getFormattedTimestamp();
        uksort($parameters, 'strcmp');
        $this->createServiceUrl();
        $parameters['Signature'] = $this->signParameters($parameters);
        $parameters = $this->getParametersAsString($parameters);
        // Save these parameters in the parameters variable so that it can be returned for unit testing.
        $this->parameters = $parameters;
        return $parameters;
    }