mod_http_oauth2: Use new mod_cron API for periodic cleanup Less frequent but this isn't that important after all since, as the comment states, expired codes are not usable anyway. They're also not that large so memory usage probably doesn't matter.

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.