We have one use case, when we can create a topic `grp` through the admin panel (web).
1. After send this topic name for specific users;
2. Users subscribe on this topic and having fun;
but
3 Other users who not receive this grp topic name, can input this name in our chat app, and enter to it without invitations.
How can we prevent this joins from no invited users?
Maybe can we set some rights?