Well, well, WELL!
Turns out, none of the “solutions” worked for me.
What I ended up doing was creating my own inbound Webhook API, by the help of strapi generate (or yarn strapi generate ymmv).
I then set up a custom controller that listens for POST requests to /webhook and with an extensible lookup table, I fire certain functions depending on what specific event and model was in that request.
The events and models I am talking about of course come from the outbound webhook that I set up in the Strapi settings.
Now I have working, completely extensible, completely secure code, that can be set up to listen to each and every thinkable action performed in the Content Manager and act accordingly 
There really are no limits to what you can use this for, but for me, I wanted to be able to enrich address information behind the scenes with coordinates from OpenStreetMap, when a user clicks Save or Create, and it works beautifully!