I would love the possibility to put a password on an online room. Sometimes its fun to fly with your friends, and when spots gets taken by random joiners. All the friends cant join (since we can be max 10 in a session.)
1.406 brought a kind of protected rooms. Players can now make private rooms that are not visible in the server listings, to join these rooms you will need to have the exact name of the server from the host, type it into the room name and click join.
I wanted to keep it simple, so the room name is the password itself. Name it for example 'Andys-Meeting' and your friends have to type in these name into the room name. Then they can join.