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.

# Introduction

This module sends a [version query][xep0092] to clients when they
connect, and logs the response, allowing statistics of client usage to
be recorded.

Note that since this is per connection, there will be a bias towards
mobile clients on bad connections.

## Example

    info    Running Running Swift version 4.0