It's an idea kinda like private chest. You can put a sign beside a door and write: [Private]Your NameOther Person's NameThen the sign would get "glued to the door" and only those people could open the door. The only person that could destroy the sign is the person that made it.
LWC does this very well. use this: /lwc -c private miauw62 Triggerlive then left click the door. this will make only us able to open the door, you can do it whit more people if you want.
I assume since LWC is using chat commands as opposed to signs, it is using either a flat file or a db. If it's a flat file, as I've seen many other mods doing, it can become unwieldy with high usage.