Create user and pass for authentication

I am following this link Self-Hosting Guide - Docker | Jitsi Meet to create a user and pass but I would like to know if there is a manual approach to this.
That is can I edit prosody.cfg.lua file to add a user and password? If so, how?

prosodyctl register USERNAME server.domain.tld PASSWORD

Thank you yes I am doing that. But I would like to know where are all users and passwords located? Are they written to a file?