mod_pubsub_post: Restructure authentication and authorization (BC) This deprecates the default "superuser" actor model and makes the default equivalent to the previous "request.id". A single actor and secret per node is supported because HTTP and WebHooks don't normally include any authorization identity. Allowing authentication bypass when no secret is given should be relatively safe when the actor is unprivileged, as will be unless explicitly configured otherwise.

This module adds a command to `prosodyctl` for listing users.

``` sh
prosodyctl mod_listusers
```