Join mode for an event ActivityPub representation (free, restricted, invite)
Currently uses our proprietary property:
"joinMode": "free"|"restricted"|"invite"
Schema.org only has isAccessibleForFree which is not even saying if it's free
as in "Free beer" or "Free to go".
Things we can probably explore in the future:
- Litepub Capability Enforcement (seems abandoned)
- OcapPub
- Bearcaps (thread on SocialHub)