mod_http_oauth2: Fix treatment of 'redirect_uri' parameter in code flow It's optional and the one stored in the client registration should really be used instead. RFC 6749 says an URI provided as parameter MUST be validated against the stored one but does not say how. Given that the client needs their secret to proceed, it seems fine to leave this for later.

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.