I want to limit the number of conference room an authenticated user can run concurrently at any time so that a user can not setup and run many conferences at the same time. Is it possible?
As authenticated users has the same jid, this is possible by implementing a custom prosody module.
It will be a limit for concurrent sessions on one shard. So if you have multiple shards you will need a central service of tracking those.
Here is how to access all current sessions https://github.com/jitsi/jitsi-meet/blob/5940f2890a786808ea6157e38b000c34475183d5/resources/prosody-plugins/mod_muc_size.lua#L192
Also this is an example that can be useful https://github.com/jitsi/jitsi-meet/blob/5940f2890a786808ea6157e38b000c34475183d5/resources/prosody-plugins/mod_filter_iq_rayo.lua#L107