Calling RPCs with a HTTP key via POST when a payload is provided

While checking out the new releases we stumbled upon this line mentioned in the new Unity client lib release:

Nakama: Adds support for calling RPCs with a HTTP key via POST when a payload is provided.

See Releases · heroiclabs/nakama-unity · GitHub

How does this work in practice? I could not find it mentioned in the client docs nor in the server side docs. I assume the idea here is that you can do RPC calls without first authenticating as a user? This would make things easier for us as we have a workflow where we frequently upload game data to the server, and currently this requires us to always create a dummy user on the server just for the authentication. Does this allow us to just do a direct POST call using either socket.server_key or runtime.http_key? (there are so many keys and they are used in confusing ways). Skipping the authentication step would make life easier.

The key here was to add http_key to the request URL. I had totally missed that part in the server side docs: