mod_s2s_auth_certs: Split PKIX based certificate checking from mod_s2s into new plugin

plugins/mod_s2s_auth_certs.lua

@@ -0,0 +1,45 @@
+module:set_global();
+
+local cert_verify_identity = require "util.x509".verify_identity;
+local NULL = {};
+local log = module._log;
+
+module:hook("s2s-check-certificate", function(event)
+	local session, host, cert = event.session, event.host, event.cert;
+	local conn = session.conn:socket();
+
+	if cert then
+		local chain_valid, errors;
+		if conn.getpeerverification then
+			chain_valid, errors = conn:getpeerverification();
+		elseif conn.getpeerchainvalid then -- COMPAT mw/luasec-hg
+			chain_valid, errors = conn:getpeerchainvalid();
+			errors = (not chain_valid) and { { errors } } or nil;
+		else
+			chain_valid, errors = false, { { "Chain verification not supported by this version of LuaSec" } };
+		end
+		-- Is there any interest in printing out all/the number of errors here?
+		if not chain_valid then
+			(session.log or log)("debug", "certificate chain validation result: invalid");
+			for depth, t in pairs(errors or NULL) do
+				(session.log or log)("debug", "certificate error(s) at depth %d: %s", depth-1, table.concat(t, ", "))
+			end
+			session.cert_chain_status = "invalid";
+		else
+			(session.log or log)("debug", "certificate chain validation result: valid");
+			session.cert_chain_status = "valid";
+
+			-- We'll go ahead and verify the asserted identity if the
+			-- connecting server specified one.
+			if host then
+				if cert_verify_identity(host, "xmpp-server", cert) then
+					session.cert_identity_status = "valid"
+				else
+					session.cert_identity_status = "invalid"
+				end
+				(session.log or log)("debug", "certificate identity validation result: %s", session.cert_identity_status);
+			end
+		end
+	end
+end, 509);
+