preventing client from creating rooms on the server

If your server is fully responsible for the creation and deletion of rooms and the matchmaking of players into them and...
if your server will give the client a room reservation in some way and...
if your client will only connect to the server with a room reservation using client.consumeSeatReservation and...
if you want to prevent any client from ever creating a room on the server and...
if you do not mind to use a dirty workaround...

...you can override the private (D'OH) property exposedMethods of the Server class:

const gameServer = new Server();
const tempServer = gameServer as any; // force access to private property by casting to any
tempServer.exposedMethods = []; // override property with empty array to not expose those methods anymore
gameServer.listen(port);

Yes, it is dirty, it might break in the future, it might not work for you, but it works perfectly for me and it made me giggle maniacally.