[Standards] Re: LAST CALL: XEP-0421 (Anonymous unique occupant identifiers for MUCs)

Also, I suspect the naive way to implement this will be to hash the bare JID. We probably want to mention that this is a bad idea and that these identifiers should be random (or we should explicitly define the security properties that are required if they're derived, which probably includes using a salt and ensuring high entropy).

The XEP suggests "One way to ensure these properties is to generate a private secret key for every room and use an HMAC algorithm with a sufficiently secure hash function to generate the occupant identifier from the real bare JID and that secret key."