$context = stream_context_create(array(
            'ssl' => array(
            'verify_peer' => false,
            'allow_self_signed' => true
            )
        ));

        $client = new SoapClient(null, array('location' => $this->url,
                                     'uri'      => $this->uri,
                                     'exceptions' => 0,
                                     'stream_context' => $context
    ));

...
 $res = $client->someFunction(new SoapVar($CredentialObject, SOAP_ENC_OBJECT));

$context = stream_context_create(array(
            'ssl' => array(
                'verify_peer' => true,
                'allow_self_signed' => false,
                'local_cert' => '/part/to/cert',
            )
        ));