public function setHttpsCertificate($localCert)
    {
        if (!is_readable($localCert)) {
            require_once 'Zend/Soap/Client/Exception.php';
            throw new Zend_Soap_Client_Exception('Invalid HTTPS client certificate path.');
        }

        $this->_local_cert = $localCert;

        $this->_soapClient = null;

        return $this;
    }