Just some notes for me, but may be useful for others.
Jitsi is a video bridge server. It allows two or more users to do video chat. It uses Prosody for an XMPP chat also, and appears to use Prosody for authentication.
User authentication file (plain text, so don't trust it)
Basically, the server name with the dots replaced with %2e
Done via prosody, using the prosodyctl command.
prosodyctl register <username> <server.example.com> <password>
replace <username> and <password> with information. Replace <server.example.com> with the (jitsi) name of the server.
You need to be using authentication (I think). Once done, authenticated users can set up pidgin as follows: