--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_muc_local_only/mod_muc_local_only.lua	Wed May 13 11:43:27 2020 +0100
@@ -0,0 +1,19 @@
+local jid = require "util.jid";
+local st = require "util.stanza";
+
+local local_rooms = module:get_option_inherited_set("muc_local_only", {});
+
+module:hook("muc-occupant-pre-join", function (event)
+	local room = event.room;
+	if not local_rooms:contains(room.jid) then
+		return; -- Not a protected room, ignore
+	end
+	local user_jid = event.occupant.bare_jid;
+	local user_host = jid.host(user_jid);
+	if not prosody.hosts[user_host] then
+		local error_reply = st.error_reply(event.stanza, "cancel", "forbidden", "This group is only available to local users", room.jid);
+		event.origin.send(error_reply);
+		return true;
+	end
+	room:set_affiliation(true, user_jid, "member", "Granting access to local user");
+end);