This is similar to how micro.blog has implemented ActivityPub support, from what I can gather. Here's their documentation from when the feature was released:
https://help.micro.blog/t/mastodon-and-activitypub/95
Oh excellent, thanks! I wonder how hard it is to make an RSS-to-ActivityPub service.
Darius Kazemi, the creator of Hometown, made an AP server where you can register a feed and it turns into an actor (ie an account): https://github.com/dariusk/rss-to-activitypub
I made my own thing, fetching an RSS feed and posting entries to an existing account. It makes the code much simpler, but is not practical if you have lots of feeds (you need yo create all accounts separately): https://sr.ht/~rakoo/rss2ap/
That's fantastic, thanks! Just what I was looking for.
I'd love it if my site's posts were ActivityPub posts, with ActivityPub replies being shown on the site as comments. I think that would be an amazing thing, but it's currently not very easy to do.
I guess I better get coding again.