Aerys\Response::setStatus PHP Method

    public function setStatus(int $code) : Response;

 public function onHandshake(Request $request, Response $response)
 {
     // During handshakes, you should always check the origin header, otherwise any site will
     // be able to connect to your endpoint. Websockets are not restricted by the same-origin-policy!
     $origin = $request->getHeader("origin");
     if ($origin !== "http://localhost:1337") {
         $response->setStatus(403);
         $response->send("<h1>origin not allowed</h1>");
         return null;
     }
     // returned values will be passed to onOpen, that way you can pass cookie values or the whole request object.
     return $request->getConnectionInfo()["client_addr"];
 }