Hi.
On headless server, first connected user controls the game. However, he is unable to block or kick connected user. It is also impossible to close port (Network --> Closed), it re-opens automatically.
Luckily, we had no much malicious users so far, but e.g. today user called "noob" intentionally attacks allies, and we had no way to kick him. We started another game on headless, and he connected too, and again, we had no way to kick him.
By the way I made him other team just before the game started, so we were smarter :-)
Thanks a lot