mod_http_oauth2: Reject unparsable URLs
This used to be caught by luaPattern=https:// in the schema but that's
been removed for some reason
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.