private function parameters()
    {
        if (!isset($this->_parameters)) {
            $parser = new SignatureParametersParser($this->signatureHeader());
            $this->_parameters = $parser->parse();
        }

        return $this->_parameters;
    }
private function parameters()
    {
        if (!isset($this->_parameters)) {
            $parser = new SignatureParametersParser($this->signatureHeader());
            $this->_parameters = $parser->parse();
        }

        return $this->_parameters;
    }
@return array

@throws Exception