seppo/doc/activitypub

https://www.w3.org/TR/activitypub/#actor-objects

https://socialhub.activitypub.rocks/t/map-terms-of-e-g-mastodon-pleroma-to-ap/2451

https://blog.joinmastodon.org/2018/06/how-to-implement-a-basic-activitypub-server/

https://tinysubversions.com/notes/reading-activitypub/#server-to-server-interactions