MT#15303 add mod_limit_auth

http://modules.prosody.im/mod_limit_auth.html

limit_auth_period = 30 -- over 30 seconds
limit_auth_max = 5 -- tolerate no more than 5 failed attempts

Change-Id: I44932d643f124991948a26c2d80c8b40a9c155d2
(cherry picked from commit f672d8e3ec)

plugins/mod_limit_auth.lua

@@ -0,0 +1,57 @@
+-- mod_limit_auth
+
+local st = require"util.stanza";
+local new_throttle = require "util.throttle".create;
+
+local period = math.max(module:get_option_number(module.name.."_period", 30), 0);
+local max = math.max(module:get_option_number(module.name.."_max", 5), 1);
+
+local tarpit_delay = module:get_option_number(module.name.."_tarpit_delay", nil);
+if tarpit_delay then
+	local waiter = require "util.async".waiter;
+	local delay = tarpit_delay;
+	function tarpit_delay()
+		local wait, done = waiter();
+		module:add_timer(delay, done);
+		wait();
+	end
+else
+	function tarpit_delay() end
+end
+
+local throttles = module:shared"throttles";
+
+local reply = st.stanza("failure", { xmlns = "urn:ietf:params:xml:ns:xmpp-sasl" }):tag("temporary-auth-failure");
+
+local function get_throttle(ip)
+	local throttle = throttles[ip];
+	if not throttle then
+		throttle = new_throttle(max, period);
+		throttles[ip] = throttle;
+	end
+	return throttle;
+end
+
+module:hook("stanza/urn:ietf:params:xml:ns:xmpp-sasl:auth", function (event)
+	local origin = event.origin;
+	if not get_throttle(origin.ip):peek(1) then
+		origin.log("warn", "Too many authentication attepmts for ip %s", origin.ip);
+		tarpit_delay();
+		origin.send(reply);
+		return true;
+	end
+end, 10);
+
+module:hook("authentication-failure", function (event)
+	get_throttle(event.session.ip):poll(1);
+end);
+
+module:add_timer(14400, function (now)
+	local old = now - 86400;
+	for ip, throttle in pairs(throttles) do
+		if throttle.t < old then
+			throttles[ip] = nil;
+		end
+	end
+end);
+