Hi,
mit der Serverstartoption "-exclusivejoin" und einer Datei in der die Steam IDs, der Leute, die auf den Server joinen können, stehen
Hier sind die Infos aus der offi. Wiki dazu:
exclusivejoin
All
Activate a whitelist only mode on the server that only lets players
join if added to the allow list. Not to be confused with "Admin
Whitelisting" which uses "AllowedCheaterSteamIDs.txt" to allow players
to cheat. This option uses "PlayersJoinNoCheckList.txt" to allow people
to join but not give them cheats. If the file does not exist in your
Linux/Win64 Binaries folder, create it and add the Steam64 IDs of the
players you wish to be allowed to join your server. Path;
"\ShooterGame\Binaries\Win64\" "/ShooterGame/Binaries/Linux/".
You will need to restart your server, if you add new lines to the file while it is running. You can however use "Cheat AllowPlayerToJoinNoCheck 12345678901234567" in game, to add a new player to the whitelist. This method will also save to the file, so you don't need to reboot the server.