--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_restrict_federation/mod_restrict_federation.lua	Thu Sep 25 13:09:57 2025 +0100
@@ -0,0 +1,67 @@
+local jid_node = require "prosody.util.jid".node;
+local st = require "prosody.util.stanza";
+
+local get_user_role = require "prosody.core.usermanager".get_user_role;
+
+function check_outgoing_stanza(event)
+	local origin, stanza = event.origin, event.stanza;
+
+	if not origin or origin.type ~= "c2s" then
+		-- We only filter user-originated traffic, so
+		-- pass this through.
+		return;
+	end
+
+	if module:may("xmpp:federate", event) then
+		-- Pass through
+		return;
+	end
+
+	-- Block
+	module:log("debug", "Forbidding outgoing %s stanza from <%s> to <%s>", stanza.name, stanza.attr.from, stanza.attr.to);
+	local err_reply = st.error_reply(event.stanza, "auth", "policy-violation", "Communication with remote domains is not permitted");
+	origin.send(err_reply);
+	return true;
+end
+
+function check_incoming_stanza(event)
+	local origin, stanza = event.origin, event.stanza;
+
+	if origin.type ~= "s2sin" then
+		-- We only filter incoming traffic from remote domains
+		-- Pass through
+		return;
+	end
+
+	local recipient_username = jid_node(stanza.attr.to);
+	if not recipient_username then
+		return;
+	end
+
+	local recipient_role, role_err = get_user_role(recipient_username, module.host);
+	if not recipient_role then
+		module:log("warn", "Unable to determine recipient role: %s", role_err);
+		-- No idea what the role is, we'll pass it through
+		return;
+	end
+
+	if recipient_role:may("xmpp:federate") then
+		-- Allowed, pass through
+		return;
+	end
+
+	-- Block
+	module:log("debug", "Forbidding incoming %s stanza from <%s> to <%s>", stanza.name, stanza.attr.from, stanza.attr.to);
+	local err_reply = st.error_reply(event.stanza, "cancel", "service-unavailable");
+	origin.send(err_reply);
+	return true;
+end
+
+module:hook("message/bare", check_incoming_stanza, 500);
+module:hook("message/full", check_incoming_stanza, 500);
+module:hook("presence/bare", check_incoming_stanza, 500);
+module:hook("presence/full", check_incoming_stanza, 500);
+module:hook("iq/bare", check_incoming_stanza, 500);
+module:hook("iq/full", check_incoming_stanza, 500);
+
+module:hook("route/remote", check_outgoing_stanza, 500);