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/Federation/Actors/LocalActorService.cs

@@ -29,6 +29,8 @@ namespace PrivaPub.Federation.Actors
 		public bool Discoverable { get; init; } = true;
 		public bool ManuallyApprovesFollowers { get; init; }
 		public bool IsFederated { get; init; } = true;
+		public bool IsCircle { get; init; }
+		public bool PostingRestrictedToModerators { get; init; }
 		public bool IsBot { get; init; }
 		public bool Indexable { get; init; }
 		public AvatarSettings Settings { get; init; } = new();
@@ -44,6 +46,8 @@ namespace PrivaPub.Federation.Actors
 		public string Following => $"{Uri}/stalking";
 		public string Featured => $"{Uri}/trophies";
 		public string FeaturedTags => $"{Uri}/tattoos";
+		public string Flock => $"{Uri}/flock";
+		public string Wardens => $"{Uri}/wardens";
 		public string SharedInbox => $"{BaseAddress}/human-centipede";
 		public string Domain => new Uri(BaseAddress).Authority;
 		public string Handle => $"{UserName}@{Domain}";
@@ -219,9 +223,10 @@ namespace PrivaPub.Federation.Actors
 			ThumbnailURL = group.ThumbnailURL,
 			PrivateKeyPem = group.PrivateKey,
 			PublicKeyPem = group.PublicKey,
-			Discoverable = group.IsDiscoverable,
-			ManuallyApprovesFollowers = group.ManuallyApprovesMembers,
-			IsFederated = group.Kind == GroupKind.Community,
+			Discoverable = group.Kind == GroupKind.Community && group.IsDiscoverable,
+			ManuallyApprovesFollowers = group.Kind == GroupKind.Circle || group.ManuallyApprovesMembers,
+			IsCircle = group.Kind == GroupKind.Circle,
+			PostingRestrictedToModerators = group.PostingPolicy == PostingPolicy.Moderators,
 			Published = group.CreationDate,
 			BaseAddress = BaseAddress
 		};

PrivaPub/Federation/Controllers/PeasantsController.cs

@@ -1,4 +1,6 @@
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.Filters;
+using Microsoft.Extensions.Options;
 using Microsoft.AspNetCore.RateLimiting;
 
 using MongoDB.Entities;
@@ -15,12 +17,15 @@ using PrivaPub.Domain.Privacy;
 using PrivaPub.Federation.Actors;
 using PrivaPub.Federation.Rendering;
 using PrivaPub.Federation.Inbox;
+using PrivaPub.Federation.Signing;
+using PrivaPub.Infrastructure.Http;
+using PrivaPub.Models.Group;
 using PrivaPub.Infrastructure;
 
 namespace PrivaPub.Federation.Controllers
 {
 	[ApiController, Route("peasants")]
-	public class PeasantsController : ControllerBase
+	public class PeasantsController : ControllerBase, IAsyncActionFilter
 	{
 		const string ActivityContentType = "application/activity+json; charset=utf-8";
 		const int OutboxSize = 20;
@@ -29,10 +34,14 @@ namespace PrivaPub.Federation.Controllers
 		readonly IInboxReceiver _inbox;
 		readonly DbEntities _dbEntities;
 		readonly ILogger<PeasantsController> _logger;
+		readonly ISignedFetchAuthorizer _fetches;
+		readonly IOptionsMonitor<FederationOptions> _federation;
 
 		public PeasantsController(ILocalActorService localActors, IInboxReceiver inbox, DbEntities dbEntities,
-			ILogger<PeasantsController> logger)
+			ILogger<PeasantsController> logger, ISignedFetchAuthorizer fetches, IOptionsMonitor<FederationOptions> federation)
 		{
+			_fetches = fetches;
+			_federation = federation;
 			_localActors = localActors;
 			_inbox = inbox;
 			_dbEntities = dbEntities;
@@ -113,6 +122,34 @@ namespace PrivaPub.Federation.Controllers
 			return local is not { IsFederated: true } ? NotFound() : Activity(ActivityPubRenderer.OrderedCollection(local.Following, 0, default));
 		}
 
+		[HttpGet, Route("{actor}/flock")]
+		public async Task<IActionResult> Members(string actor, CancellationToken token)
+		{
+			var local = await _localActors.FindByUserName(actor, token);
+			if (local is not { IsFederated: true, Kind: LocalActorKind.Group })
+				return NotFound();
+			var group = await _dbEntities.Groups.MatchID(local.Id).ExecuteFirstAsync(token);
+			if (local.IsCircle && !SignedFetchAuthorizer.MayReadCircle(group, await _fetches.Requester(Request, token)))
+				return NotFound();
+			return Activity(ActivityPubRenderer.OrderedCollection(local.Flock, group.Members.Count, default));
+		}
+
+		[HttpGet, Route("{actor}/wardens")]
+		public async Task<IActionResult> Moderators(string actor, CancellationToken token)
+		{
+			var local = await _localActors.FindByUserName(actor, token);
+			if (local is not { IsFederated: true, Kind: LocalActorKind.Group })
+				return NotFound();
+			var group = await _dbEntities.Groups.MatchID(local.Id).ExecuteFirstAsync(token);
+			if (local.IsCircle && !SignedFetchAuthorizer.MayReadCircle(group, await _fetches.Requester(Request, token)))
+				return NotFound();
+			var moderators = new List<JsonNode>();
+			foreach (var member in group.Members.Where(m => !m.IsForeign && m.Role is GroupRole.Owner or GroupRole.Moderator))
+				if (await _localActors.FindById(LocalActorKind.Person, member.AvatarId, token) is { } moderator)
+					moderators.Add(moderator.Uri);
+			return Activity(ActivityPubRenderer.OrderedCollection(local.Wardens, moderators.Count, moderators));
+		}
+
 		[HttpGet, Route("{actor}/trophies")]
 		public async Task<IActionResult> Featured(string actor, CancellationToken token)
 		{
@@ -145,6 +182,12 @@ namespace PrivaPub.Federation.Controllers
 		public async Task<IActionResult> Post(string actor, string postId, CancellationToken token)
 		{
 			var (local, post) = await PublicPost(actor, postId, token);
+			if (post == default && await CirclePost(actor, postId, token) is { } circlePost)
+			{
+				var circleNote = ActivityPubRenderer.Note(circlePost.Post, circlePost.Author, circlePost.Circle, circlePost.Post.InReplyToURI);
+				circleNote["@context"] = ActivityPubRenderer.Context();
+				return Activity(circleNote);
+			}
 			if (post == default)
 				return await Tombstone(actor, postId, token) ?? NotFound();
 			if (WantsHtml())
@@ -202,6 +245,20 @@ namespace PrivaPub.Federation.Controllers
 			return (local, post);
 		}
 
+		async Task<(LocalActor Author, LocalActor Circle, PostEntity Post)?> CirclePost(string actor, string postId, CancellationToken token)
+		{
+			var local = await _localActors.FindByUserName(actor, token);
+			if (local is not { Kind: LocalActorKind.Person })
+				return default;
+			var post = await _dbEntities.Posts
+				.Match(p => p.ID == postId && p.GroupUserId == local.Id && !p.IsFederatedCopy && !p.DeletedAt.HasValue && p.Visibility == PostVisibility.Circle)
+				.ExecuteFirstAsync(token);
+			var circle = post == default ? default : await _dbEntities.Groups.MatchID(post.GroupId).ExecuteFirstAsync(token);
+			if (circle == default || !SignedFetchAuthorizer.MayReadCircle(circle, await _fetches.Requester(Request, token)))
+				return default;
+			return (local, _localActors.FromGroup(circle), post);
+		}
+
 		async Task<IActionResult> Tombstone(string actor, string postId, CancellationToken token)
 		{
 			var local = await _localActors.FindByUserName(actor, token);
@@ -257,6 +314,19 @@ namespace PrivaPub.Federation.Controllers
 				&& !accept.Contains("ld+json", StringComparison.OrdinalIgnoreCase);
 		}
 
+		[NonAction]
+		public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
+		{
+			if (_federation.CurrentValue.SecureMode && HttpMethods.IsGet(Request.Method)
+				&& !string.Equals(context.RouteData.Values["actor"] as string, LocalActorService.InstanceUserName, StringComparison.OrdinalIgnoreCase)
+				&& await _fetches.Requester(Request, HttpContext.RequestAborted) == default)
+			{
+				context.Result = StatusCode(StatusCodes.Status401Unauthorized);
+				return;
+			}
+			await next();
+		}
+
 		IActionResult Answer(InboxResult result)
 		{
 			if (result.Error != default)

PrivaPub/Federation/Inbox/Handlers/AnnounceHandler.cs

@@ -26,9 +26,11 @@ namespace PrivaPub.Federation.Inbox.Handlers
 		readonly ILocalActorService _localActors;
 		readonly IRemotePosts _remotePosts;
 		readonly IFanout _fanout;
+		readonly IRemoteActorService _remoteActors;
 
-		public AnnounceHandler(DbEntities dbEntities, ILocalActorService localActors, IRemotePosts remotePosts, IFanout fanout)
+		public AnnounceHandler(DbEntities dbEntities, ILocalActorService localActors, IRemotePosts remotePosts, IFanout fanout, IRemoteActorService remoteActors)
 		{
+			_remoteActors = remoteActors;
 			_dbEntities = dbEntities;
 			_localActors = localActors;
 			_remotePosts = remotePosts;
@@ -41,7 +43,10 @@ namespace PrivaPub.Federation.Inbox.Handlers
 		{
 			var inner = activity["object"];
 			if (inner is JsonObject && Value(inner, "type") is "Create" or "Update" or "Delete" or "Like" or "Dislike" or "Undo" or "Add" or "Remove" or "Block")
+			{
+				await GroupActivity(inner, actor, token);
 				return;
+			}
 			var objectUri = Id(inner);
 			var announceId = Id(activity);
 			if (objectUri == default || announceId == default)
@@ -96,6 +101,66 @@ namespace PrivaPub.Federation.Inbox.Handlers
 			await _fanout.Distribute(reblog, token);
 		}
 
+		async Task GroupActivity(JsonNode inner, ForeignAvatar group, CancellationToken token)
+		{
+			if (group.AvatarType != AvatarType.Group
+				|| !await _dbEntities.Followings.Match(f => f.TargetActorURI == group.ActorURI && f.State == FollowState.Accepted).ExecuteAnyAsync(token))
+				return;
+			var objectUri = Id(inner["object"]);
+			switch (Value(inner, "type"))
+			{
+				case "Create" when objectUri != default:
+					if (await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri).ExecuteAnyAsync(token))
+						return;
+					var post = await _remotePosts.StoreContext(objectUri, 0, token);
+					if (post == default)
+						return;
+					await DB.Default.Update<PostEntity>().MatchID(post.ID).Modify(p => p.AudienceURI, group.ActorURI).ExecuteAsync(token);
+					post.AudienceURI = group.ActorURI;
+					await _fanout.Distribute(post, token);
+					break;
+				case "Update" when objectUri != default:
+					var stored = await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri && p.AudienceURI == group.ActorURI && !p.DeletedAt.HasValue)
+						.ExecuteFirstAsync(token);
+					if (stored == default)
+						return;
+					using (var fetched = await _remoteActors.FetchObject(objectUri, token))
+					{
+						var note = fetched == default ? default : NoteParser.Parse(System.Text.Json.Nodes.JsonNode.Parse(fetched.Root.GetRawText()));
+						if (note == default || note.AttributedTo != stored.ActorURI)
+							return;
+						stored.Revisions.Add(new PostRevision
+						{
+							Title = stored.Title,
+							SpoilerText = stored.SpoilerText,
+							ContentHtml = stored.ContentHtml,
+							HasContentWarning = stored.HasContentWarning,
+							EditedAt = stored.EditedAt ?? stored.CreationDate
+						});
+						stored.Title = note.Title;
+						stored.SpoilerText = note.SpoilerText;
+						stored.HasContentWarning = note.Sensitive;
+						stored.Text = note.ContentHtml;
+						stored.ContentHtml = note.ContentHtml;
+						stored.Tags = note.Tags.ToList();
+						stored.Media = note.Attachments.ToList();
+						stored.EditedAt = note.Updated ?? DateTime.UtcNow;
+						await DB.Default.SaveAsync(stored, token);
+					}
+					break;
+				case "Delete" when objectUri != default:
+					var deleted = await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri && p.AudienceURI == group.ActorURI).ExecuteFirstAsync(token);
+					if (deleted == default)
+						return;
+					using (var check = await _remoteActors.FetchObject(objectUri, token))
+						if (check != default && Value(System.Text.Json.Nodes.JsonNode.Parse(check.Root.GetRawText()), "type") != "Tombstone")
+							return;
+					await DB.Default.DeleteAsync<PostEntity>(deleted.ID);
+					await DB.Default.DeleteAsync<TimelineEntry>(e => e.PostId == deleted.ID);
+					break;
+			}
+		}
+
 		static List<string> Strings(JsonNode node) => node switch
 		{
 			JsonArray array => array.Select(Id).Where(id => id != default).ToList(),

PrivaPub/Federation/Inbox/Handlers/CreateHandler.cs

@@ -33,10 +33,12 @@ namespace PrivaPub.Federation.Inbox.Handlers
 		readonly IDomainBlocks _domainBlocks;
 		readonly IFanout _fanout;
 		readonly IRemotePosts _remotePosts;
+		readonly IGroupDistributor _groups;
 
 		public CreateHandler(DbEntities dbEntities, ILocalActorService localActors, IRemoteActorService remoteActors, IDeliveryService delivery,
-			IDomainBlocks domainBlocks, IFanout fanout, IRemotePosts remotePosts)
+			IDomainBlocks domainBlocks, IFanout fanout, IRemotePosts remotePosts, IGroupDistributor groups)
 		{
+			_groups = groups;
 			_fanout = fanout;
 			_remotePosts = remotePosts;
 			_dbEntities = dbEntities;
@@ -85,10 +87,17 @@ namespace PrivaPub.Federation.Inbox.Handlers
 			var parent = string.IsNullOrEmpty(note.InReplyTo)
 				? default
 				: await _dbEntities.Posts.Match(p => p.ObjectURI == note.InReplyTo && !p.DeletedAt.HasValue).ExecuteFirstAsync(token);
-			var group = visibility is PostVisibility.Public or PostVisibility.Unlisted
-				? localTargets.FirstOrDefault(t => t.Kind == LocalActorKind.Group)
-				: default;
-			if (group != default && !await IsAcceptedFollower(group, author.ActorURI, token))
+			var circle = localTargets.FirstOrDefault(t => t is { Kind: LocalActorKind.Group, IsCircle: true });
+			if (circle != default)
+			{
+				if (!await IsCircleMember(circle, author.ActorURI, token))
+					return;
+				visibility = PostVisibility.Circle;
+			}
+			var group = circle ?? (visibility is PostVisibility.Public or PostVisibility.Unlisted
+				? localTargets.FirstOrDefault(t => t is { Kind: LocalActorKind.Group, IsCircle: false })
+				: default);
+			if (group is { IsCircle: false } && !await MayPost(group, author.ActorURI, token))
 				group = default;
 
 			var repliesToLocal = parent is { IsFederatedCopy: false } && visibility != PostVisibility.Direct;
@@ -128,11 +137,22 @@ namespace PrivaPub.Federation.Inbox.Handlers
 			await _fanout.Distribute(post, token);
 			if (conversation != default)
 				await DB.Default.Update<DmGroup>().MatchID(conversation.ID).Modify(g => g.UpdatedAt, DateTime.UtcNow).ExecuteAsync(token);
-			if (group != default)
+			if (group is { IsCircle: false })
+				await _groups.Announce(group, activity.AsObject(), note.Id, isNewPost: string.IsNullOrEmpty(note.InReplyTo), token);
+		}
+
+		async Task<bool> IsCircleMember(LocalActor circle, string actorUri, CancellationToken token) =>
+			await _dbEntities.Groups.Match(g => g.ID == circle.Id && g.Members.Any(m => m.IsForeign && m.AvatarId == actorUri)).ExecuteAnyAsync(token);
+
+		async Task<bool> MayPost(LocalActor community, string actorUri, CancellationToken token)
+		{
+			var entity = await _dbEntities.Groups.MatchID(community.Id).ExecuteFirstAsync(token);
+			return entity?.PostingPolicy switch
 			{
-				var announce = ActivityPubRenderer.Announce(group, note.Id, $"announce-{post.ID}");
-				await _delivery.EnqueueToFollowers(group, announce, token);
-			}
+				PostingPolicy.Anyone => true,
+				PostingPolicy.Followers => await IsAcceptedFollower(community, actorUri, token),
+				_ => false
+			};
 		}
 
 		async Task<DmGroup> FindOrCreateConversation(List<string> participantUris, string context, CancellationToken token)

PrivaPub/Federation/Inbox/Handlers/DeleteHandler.cs

@@ -26,9 +26,12 @@ namespace PrivaPub.Federation.Inbox.Handlers
 		readonly ILocalActorService _localActors;
 		readonly IRemoteActorService _remoteActors;
 		readonly IDeliveryService _delivery;
+		readonly IGroupDistributor _groups;
 
-		public DeleteHandler(DbEntities dbEntities, ILocalActorService localActors, IRemoteActorService remoteActors, IDeliveryService delivery)
+		public DeleteHandler(DbEntities dbEntities, ILocalActorService localActors, IRemoteActorService remoteActors, IDeliveryService delivery,
+			IGroupDistributor groups)
 		{
+			_groups = groups;
 			_dbEntities = dbEntities;
 			_localActors = localActors;
 			_remoteActors = remoteActors;
@@ -67,6 +70,8 @@ namespace PrivaPub.Federation.Inbox.Handlers
 				return;
 			await DB.Default.DeleteAsync<PostEntity>(post.ID);
 			await DB.Default.DeleteAsync<TimelineEntry>(e => e.PostId == post.ID || e.ReblogOfPostId == post.ID);
+			if (!string.IsNullOrEmpty(post.GroupId) && await _localActors.FindById(LocalActorKind.Group, post.GroupId, token) is { IsCircle: false } community)
+				await _groups.Announce(community, activity.AsObject(), post.ObjectURI, isNewPost: false, token);
 			await DB.Default.DeleteAsync<PostEntity>(p => p.ReblogOfPostId == post.ID);
 			if (!string.IsNullOrEmpty(post.AnsweringToPostId))
 				await DB.Default.Update<PostEntity>().MatchID(post.AnsweringToPostId).Modify(b => b.Inc(p => p.RepliesCount, -1)).ExecuteAsync(token);

PrivaPub/Federation/Inbox/Handlers/UpdateHandler.cs

@@ -2,6 +2,7 @@ using MongoDB.Entities;
 
 using PrivaPub.Federation.Actors;
 using PrivaPub.Federation.Objects;
+using PrivaPub.Federation.Outbox;
 using PrivaPub.Models.Post;
 using PrivaPub.Models.User;
 using PrivaPub.StaticServices;
@@ -21,9 +22,11 @@ namespace PrivaPub.Federation.Inbox.Handlers
 		readonly DbEntities _dbEntities;
 		readonly ILocalActorService _localActors;
 		readonly IRemoteActorService _remoteActors;
+		readonly IGroupDistributor _groups;
 
-		public UpdateHandler(DbEntities dbEntities, ILocalActorService localActors, IRemoteActorService remoteActors)
+		public UpdateHandler(DbEntities dbEntities, ILocalActorService localActors, IRemoteActorService remoteActors, IGroupDistributor groups)
 		{
+			_groups = groups;
 			_dbEntities = dbEntities;
 			_localActors = localActors;
 			_remoteActors = remoteActors;
@@ -79,6 +82,8 @@ namespace PrivaPub.Federation.Inbox.Handlers
 			post.EditedAt = note.Updated ?? DateTime.UtcNow;
 			post.UpdateDate = DateTime.UtcNow;
 			await DB.Default.SaveAsync(post, token);
+			if (!string.IsNullOrEmpty(post.GroupId) && await _localActors.FindById(Models.Federation.LocalActorKind.Group, post.GroupId, token) is { IsCircle: false } community)
+				await _groups.Announce(community, activity.AsObject(), post.ObjectURI, isNewPost: false, token);
 		}
 	}
 }

PrivaPub/Federation/Outbox/GroupDistributor.cs

@@ -0,0 +1,48 @@
+using PrivaPub.Federation.Actors;
+using PrivaPub.Federation.Rendering;
+
+using System.Security.Cryptography;
+using System.Text;
+using System.Text.Json.Nodes;
+
+namespace PrivaPub.Federation.Outbox
+{
+	public interface IGroupDistributor
+	{
+		Task Announce(LocalActor group, JsonObject activity, string objectUri, bool isNewPost, CancellationToken token);
+	}
+
+	public class GroupDistributor : IGroupDistributor
+	{
+		readonly IDeliveryService _delivery;
+
+		public GroupDistributor(IDeliveryService delivery)
+		{
+			_delivery = delivery;
+		}
+
+		public async Task Announce(LocalActor group, JsonObject activity, string objectUri, bool isNewPost, CancellationToken token)
+		{
+			if (group is not { IsCircle: false, Kind: Models.Federation.LocalActorKind.Group })
+				return;
+			var embedded = (JsonObject)activity.DeepClone();
+			embedded.Remove("@context");
+			embedded["audience"] ??= group.Uri;
+			var key = Convert.ToHexStringLower(SHA256.HashData(Encoding.UTF8.GetBytes(activity["id"]?.GetValue<string>() ?? embedded.ToJsonString())))[..24];
+			var announce = new JsonObject
+			{
+				["@context"] = ActivityPubRenderer.Context(),
+				["id"] = group.ActivityUri($"announce-{key}"),
+				["type"] = "Announce",
+				["actor"] = group.Uri,
+				["to"] = new JsonArray(ActivityPubRenderer.Public),
+				["cc"] = new JsonArray(group.Followers),
+				["audience"] = group.Uri,
+				["object"] = embedded
+			};
+			await _delivery.EnqueueToFollowers(group, announce, token);
+			if (isNewPost && !string.IsNullOrEmpty(objectUri))
+				await _delivery.EnqueueToFollowers(group, ActivityPubRenderer.Announce(group, objectUri, $"announce-object-{key}"), token);
+		}
+	}
+}

PrivaPub/Federation/Outbox/OutboxPublisher.cs

@@ -32,8 +32,10 @@ namespace PrivaPub.Federation.Outbox
 
 		public async Task<IReadOnlyList<string>> Audience(LocalActor author, PostEntity post, CancellationToken token)
 		{
-			if (post.Visibility is PostVisibility.Circle or PostVisibility.LocalGeo || post.IsLocalOnly)
+			if (post.Visibility == PostVisibility.LocalGeo || post.IsLocalOnly)
 				return Array.Empty<string>();
+			if (post.Visibility == PostVisibility.Circle)
+				return await CircleMembers(post.GroupId, token);
 
 			var inboxes = new List<string>();
 			if (post.Visibility is PostVisibility.Public or PostVisibility.Unlisted or PostVisibility.FollowersOnly)
@@ -58,16 +60,21 @@ namespace PrivaPub.Federation.Outbox
 					inboxes.Add(parentAuthor.InboxURL);
 			}
 
-			if (!string.IsNullOrEmpty(post.GroupId) && post.Visibility is PostVisibility.Public or PostVisibility.Unlisted)
-			{
-				var group = await _localActors.FindById(LocalActorKind.Group, post.GroupId, token);
-				if (group is { IsFederated: true })
-					inboxes.AddRange(await _delivery.FollowerInboxes(group, token));
-			}
-
 			return inboxes.Where(i => !string.IsNullOrEmpty(i)).Distinct(StringComparer.Ordinal).ToList();
 		}
 
+		async Task<IReadOnlyList<string>> CircleMembers(string groupId, CancellationToken token)
+		{
+			var circle = string.IsNullOrEmpty(groupId) ? default : await _dbEntities.Groups.MatchID(groupId).ExecuteFirstAsync(token);
+			if (circle == default)
+				return Array.Empty<string>();
+			var remote = circle.Members.Where(m => m.IsForeign).Select(m => m.AvatarId).ToList();
+			if (remote.Count == 0)
+				return Array.Empty<string>();
+			return (await _dbEntities.ForeignAvatars.Match(a => remote.Contains(a.ActorURI)).ExecuteAsync(token))
+				.Select(a => a.InboxURL).Where(i => !string.IsNullOrEmpty(i)).Distinct(StringComparer.Ordinal).ToList();
+		}
+
 		public async Task Publish(LocalActor author, PostEntity post, JsonObject activity, CancellationToken token)
 		{
 			var inboxes = await Audience(author, post, token);

PrivaPub/Federation/Rendering/ActivityPubRenderer.cs

@@ -109,17 +109,25 @@ namespace PrivaPub.Federation.Rendering
 			var mentions = post.Mentions.Select(m => (JsonNode)m.ActorURI).ToArray();
 			var (to, cc) = post.Visibility switch
 			{
+				PostVisibility.Circle when group != default => (new JsonArray(group.Uri, group.Flock), new JsonArray(mentions)),
 				PostVisibility.Unlisted => (new JsonArray(author.Followers), new JsonArray(mentions.Prepend(Public).ToArray())),
 				PostVisibility.FollowersOnly => (new JsonArray(author.Followers), new JsonArray(mentions)),
 				PostVisibility.Direct => (new JsonArray(mentions), new JsonArray()),
 				_ => (new JsonArray(Public), new JsonArray(mentions.Prepend(author.Followers).ToArray()))
 			};
-			if (group != default)
+			if (group is { IsCircle: false })
 				cc.Add(group.Uri);
 
 			var note = NoteBody(post, author, to, cc, inReplyTo);
 			if (group != default)
 				note["audience"] = group.Uri;
+			else if (!string.IsNullOrEmpty(post.AudienceURI))
+				note["audience"] = post.AudienceURI;
+			if (group is { IsCircle: false } && string.IsNullOrEmpty(inReplyTo))
+			{
+				note["type"] = "Page";
+				note["name"] = post.Title ?? Headline(post);
+			}
 			return note;
 		}
 
@@ -141,6 +149,13 @@ namespace PrivaPub.Federation.Rendering
 			return note;
 		}
 
+		static string Headline(PostEntity post)
+		{
+			var text = System.Text.RegularExpressions.Regex.Replace(post.ContentHtml ?? post.Text ?? string.Empty, "<[^>]+>", " ");
+			text = WebUtility.HtmlDecode(System.Text.RegularExpressions.Regex.Replace(text, "\\s+", " ")).Trim();
+			return text.Length <= 100 ? text : text[..97] + "...";
+		}
+
 		static JsonObject NoteBody(PostEntity post, LocalActor author, JsonArray to, JsonArray cc, string inReplyTo)
 		{
 			var content = post.ContentHtml ?? Html(post.Text);

PrivaPub/Federation/Signing/SignedFetchAuthorizer.cs

@@ -0,0 +1,40 @@
+using PrivaPub.Federation.Actors;
+using PrivaPub.Federation.Objects;
+using PrivaPub.Models.User;
+
+using GroupEntity = PrivaPub.Models.Group.Group;
+
+namespace PrivaPub.Federation.Signing
+{
+	public interface ISignedFetchAuthorizer
+	{
+		Task<ForeignAvatar> Requester(HttpRequest request, CancellationToken token);
+	}
+
+	public class SignedFetchAuthorizer : ISignedFetchAuthorizer
+	{
+		readonly IRemoteActorService _remoteActors;
+
+		public SignedFetchAuthorizer(IRemoteActorService remoteActors)
+		{
+			_remoteActors = remoteActors;
+		}
+
+		public async Task<ForeignAvatar> Requester(HttpRequest request, CancellationToken token)
+		{
+			var parameters = HttpSignatures.Parse(request.Headers["Signature"].ToString());
+			if (parameters == default || HttpSignatures.CheckRequest(request, parameters, body: default) != default)
+				return default;
+			var signingString = HttpSignatures.SigningString(request, parameters);
+			var actor = await _remoteActors.GetActorByKeyId(parameters.KeyId, refresh: false, token);
+			if (actor != default && HttpSignatures.Verify(actor.PublicKey, signingString, parameters.Signature))
+				return actor;
+			actor = await _remoteActors.GetActorByKeyId(parameters.KeyId, refresh: true, token);
+			return actor != default && HttpSignatures.Verify(actor.PublicKey, signingString, parameters.Signature) ? actor : default;
+		}
+
+		public static bool MayReadCircle(GroupEntity circle, ForeignAvatar requester) =>
+			requester != default && circle.Members.Any(m => m.IsForeign
+				&& (m.AvatarId == requester.ActorURI || requester.AvatarType == AvatarType.Application && Origin.Same(m.AvatarId, requester.ActorURI)));
+	}
+}