mod_http_oauth2: Return Authentication Time per OpenID Core Section 2 Mandatory To Implement, either MUST include or OPTIONAL depending on things we don't look at, so might as well include it all the time. Since we do not persist authentication state with cookies or such, the authentication time will always be some point between the user being sent to the authorization endpoint and the time they are sent back to the client application.

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.