Is it possible to limit access to an event room?

Yes, you can create password- or token-protected event rooms, so only participants with the password or token can join. To set a password or token, click Actions → Edit to the right of the room name. Choose access type – Password or Token – and click Save event.

The password is the same for all participants. For token-protected events, each participant receives a unique token that only one person can use to enter the event.