mod_http_oauth2: Always show early errors to user Before having validated the client_id, communicating an error back to the client via redirect would make this an open redirect, so we may just as well skip past that logic, and especially the warning log message.

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.