$context = stream_context_create([
    'ssl' => [
        // set some SSL/TLS specific options
        'verify_peer' => false,
        'verify_peer_name' => false,
        'allow_self_signed' => true
    ]
]);

$client  = new SoapClient(null, [
    'location' => 'https://...',
    'uri' => '...', 
    'stream_context' => $context
]);