我要发送包含pem文件的xml请求wia soap客户端。

PHP 7.0

$xmlReq = 'my xml string'; // xml

$location_URL="https://server.com/raws";
        $certificate = 'path/to/file.pem';
        $password = '123456';

        $client = new SoapClient(null,array(
            'location' => $location_URL,'uri'      => $location_URL,'trace'    => true,'exceptions'=> true,'keep_alive'    => true,'cache_wsdl' => WSDL_CACHE_NONE,'encoding' => 'utf-8','local_cert'    => $certificate,'passphrase'    => $password
        ));

$search_result = $client->__doRequest($xmlReq,$location_URL,SOAP_1_2);

请告诉我如何发送带有pem文件的请求（原始xml）。