Damn... Fedify is really good. It seems like the ActivityPub library I always wanted for Node applications (rather than a reference server like the one I created for ExpressJS).

I love that it's built so you can take an existing app and quickly drop in the federation features you need (like oh okay I need my application to Follow/Accept/Reject/Undo and have the ability to Create an Article but that's it, cool, Fedify has me covered)

https://fedify.dev/tutorial/basics