For deployments that have https://hg.prosody.im/trunk/file/tip/plugins/muc/register.lib.lua#l7 and use https://modules.prosody.im/mod_muc_http_auth.html users can still register to a MUC even if they are not allowed to join. That means they would receive RAI or RMN, for instance.

This module writes out a traceback to `traceback.txt` in Prosodys data
directory (see `prosodyctl about`) when the signal `SIGUSR1` is
received. This is useful when debugging seemingly frozen instances in
case it is stuck in Lua code.