{
  "@context": "https://www.w3.org/ns/activitystreams",
  "id": "https://site/unique",
  "type": ["Like", "http://schema.org/LikeAction"]
  "actor": "http://www.test.example/martin",
  "object": "http://example.org/foo.jpg"
  }

https://www.w3.org/TR/activitystreams-core/

mime-type application/activity+json

https://w3c-dvcg.github.io/ld-signatures/#linked-data-signature-overview

https://tools.ietf.org/html/draft-cavage-http-signatures-10


https://raw.githubusercontent.com/w3c/activitypub/gh-pages/activitypub-tutorial.txt

  aaronpk | so what they did is they made keyId be a URL to an activitypub profile