SOAP无法使用SSL中的SSL证书连接到主机

Question

我正在尝试使用 .PEM 证书发送SOAP请求。它会抛出异常

SoapFault exception: [HTTP] Could not connect to host.

我正在发送像这样的SOAP请求

$params = array('trace' => 1,'exceptions' => 1, 
            'soap_version' => SOAP_1_1, 'cache_wsdl' => WSDL_CACHE_NONE,
             'local_cert'=>'filename.pem'); // The SOAP File and Certificate file is in same Folder.So i didnt given any path. I tried with full path also.

   $url="filename.wsdl";
   $username="xxxx";
   $password="xxxxx";

        $client=new SoapClient($url,$params);

        $response=$client->createUser($credentials,$object);

任何人帮助我解决SOAP请求调用.PEM SSL身份验证的问题。谢谢