Add an Authorize activity?

[Laurin-W]

Issue
While you can remove rights from resources or add read rights using WAC, this is not possible using ActivityPub. The only way, read rights are granted is through Create or Update activities by adding the recipients to the WAC read list.

Proposal
We could add a custom Authorize activity that lists actors which to grant or remove certain rights to / from.
Since this is non-standard it might be good, to keep in touch with the AP community.