@jdlh

Important question:

For good reasons, it is not part of ActivityPub!

ActivityPub does neither define https as a MUST transport mechanism (you can use it from toaster to toothbrush ot peer-to-peer, via ipfs or whatever) –
nor does it define being webfinger a part of it.
It is in fact a convention.
The workflow is defined in https://docs.joinmastodon.org/spec/webfinger/

I think it does not promote the Open Web but is ok as an _alternative_ to my own domain.
But e.g. a Public Broadcaster should theoretically only be zdf.social instead of @ZDF