$wsdl = 'PATH/TO/WSDL';
$url = 'http://URL_TO_SOAP_SERVICE';
$cert = 'PATH/TO/CLIENT/CERT';

$context = stream_context_create([
    'ssl' => [
        'crypto_method' =>  STREAM_CRYPTO_METHOD_TLSv1_1_CLIENT,
        'verify_peer' => true,
        'verify_peer_name' => true,
        'allow_self_signed' => false,
        'cafile' => '/path/to/cafile.selfsigned'
    ]
]);

$params = [
    'location' => $url,
    'local_cert' => $cert,
    'trace' => true,
    'exceptions' => true,
    'verifypeer' => true,
    'verifyhost' => true,
    'allow_self_signed' => false,
    'connection_timeout' => 180,
    'keep_alive' => false,
    'stream_context' => $context
];

$client = new SoapClient($wsdl, $params)