Communities follow FEP-1b12, circles federate to their members only

Communities:
- a post addressed to a community (to, cc or audience) is accepted
  according to its posting policy - followers, anyone, or moderators -
  and GroupDistributor announces the whole activity with `audience` to
  the community's followers, plus the object for new posts so Mastodon
  shows them; updates and deletes of community content are announced too;
- top-level posts are Pages with a name (the title, or a headline from
  the text); /flock counts members, /wardens lists moderators;
- a Mastodon client posts into a community by mentioning it, or into a
  remote group, which sets `audience`;
- an Announce of an activity from a remote group a persona follows (Lemmy)
  is followed through: the object is fetched from its own origin, kept with
  its AudienceURI, and fanned out to the group's local followers; updates
  are applied in place and deletes checked against the origin.

Circles stop being local-only: an undiscoverable Group actor whose follows
are all requests the owner approves; posts addressed to the circle and its
/flock and delivered to members' own inboxes, never announced, never
public; a remote member's post into the circle is accepted from members
only. SignedFetchAuthorizer serves circle posts and collections only to a
signed request from a member or a member server's instance actor - 404 for
anyone else. Circles never surface in search, lookups, mentions, account
ids or profile pages.

Federation:SecureMode requires a valid signature on every GET under
/peasants except the instance actor. Group forms take a posting policy.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012CzABvBkbcFqoHdmi8b9WB

PrivaPub/Middleware/SocialPubConfigurations.cs

@@ -15,6 +15,7 @@ using PrivaPub.Services.ClientToServer.Private;
 using PrivaPub.Services.ClientToServer.Public;
 using PrivaPub.Federation.Actors;
 using PrivaPub.Federation.Outbox;
+using PrivaPub.Federation.Signing;
 using PrivaPub.Federation.Inbox;
 using PrivaPub.Federation.Moderation;
 using PrivaPub.Federation.Inbox.Handlers;
@@ -65,6 +66,8 @@ namespace PrivaPub.Middleware
 				.AddSingleton<IRemoteActorService, RemoteActorService>()
 				.AddSingleton<IDeliveryService, DeliveryService>()
 				.AddSingleton<IOutboxPublisher, OutboxPublisher>()
+				.AddSingleton<IGroupDistributor, GroupDistributor>()
+				.AddSingleton<ISignedFetchAuthorizer, SignedFetchAuthorizer>()
 				.AddSingleton<IFanout, Fanout>()
 				.AddSingleton<IInboxReceiver, InboxReceiver>()
 				.AddSingleton<IActivityHandler, FollowHandler>()