This was my experience too.

It also doesn't play very well in practice with JCS canonicalisation, as used by FEP-8b32 signatures: #^https://zotum.net/channel/fentiger?mid=d9557d63-a9e5-4bba-a39d-e2ee785def42

Trying to treat messages as "JSON-LD first" has taken me a very long way down a blind alley, and cost me a lot of time.

@silverpill

How does it check that the user is logged in? Does it present a login form?

It checks whether the user has a session cookie. Hubzilla doesn't show a login form here; it could, but that wouldn't work so well for eg image fetches.

And then, after login, which instance generates activities?

FEP-61cf only covers authenticating the user. It doesn't tackle the question of what happens when the now-authenticated user writes a post. How should that post federate outwards, in such a way that other instances can trust it? I don't know how Hubzilla approaches this; maybe @Mario Vavti can comment.