Steam Whitelisting (server.steamgroup) doesn't work?!

Hey there,

I am setting up a new server and want to whitelist only people in a certain Steam Group.
As far as I know the command server.steamgroup “103582791435321195” in the server.cfg should achieve this.

However, it doesn’t work. Anyone can just join, I tested it with some friends.

Is this bugged or something? Are there alternatives?

No quotation marks around the Steam group’s ID number.