--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/plugins/muc/hats.lib.lua	Wed Mar 18 17:42:56 2020 +0000
@@ -0,0 +1,23 @@
+local st = require "util.stanza";
+
+local xmlns_hats = "xmpp:prosody.im/protocol/hats:1";
+
+module:hook("muc-broadcast-presence", function (event)
+	-- Strip any hats claimed by the client (to prevent spoofing)
+	event.stanza:remove_children("hats", xmlns_hats);
+
+	local aff_data = event.room:get_affiliation_data(event.occupant.bare_jid);
+	local hats = aff_data and aff_data.hats;
+	if not hats then return; end
+	local hats_el;
+	for hat_id, hat_data in pairs(hats) do
+		if hat_data.active then
+			if not hats_el then
+				hats_el = st.stanza("hats", { xmlns = xmlns_hats });
+			end
+			hats_el:tag("hat", { uri = hat_id, title = hat_data.title }):up();
+		end
+	end
+	if not hats_el then return; end
+	event.stanza:add_direct_child(hats_el);
+end);

--- a/plugins/muc/mod_muc.lua	Sun Mar 15 20:35:07 2020 +0100
+++ b/plugins/muc/mod_muc.lua	Wed Mar 18 17:42:56 2020 +0000
@@ -105,6 +105,7 @@
 module:add_identity("conference", "text", module:get_option_string("name", "Prosody Chatrooms"));
 module:add_feature("http://jabber.org/protocol/muc");
 module:depends "muc_unique"
+module:require "muc/hats";
 module:require "muc/lock";
 
 local function is_admin(jid)