-- Copyright (C) 2013 - 2014 Tobias Markmann

-- This file is MIT/X11 licensed.

--

-- Implements authentication via POSH (PKIX over Secure HTTP)

-- http://tools.ietf.org/html/draft-miller-posh-03

--

module:set_global();

local json = require "util.json";

local base64 = require "util.encodings".base64;

local pem2der = require "util.x509".pem2der;

local hashes = require "util.hashes";

local build_url = require "socket.url".build;

local async = require "util.async";

local http = require "net.http";

local cache = require "util.cache".new(100);

local hash_order = { "sha-512", "sha-384", "sha-256", "sha-224", "sha-1" };

local hash_funcs = { hashes.sha512, hashes.sha384, hashes.sha256, hashes.sha224, hashes.sha1 };

local function posh_lookup(host_session, resume)

	-- do nothing if posh info already exists

	if host_session.posh ~= nil then return end

	local target_host = false;

	if host_session.direction == "incoming" then

		target_host = host_session.from_host;

	elseif host_session.direction == "outgoing" then

		target_host = host_session.to_host;

	end

	local cached = cache:get(target_host);

	if cached then

		if os.time() > cached.expires then

			cache:set(target_host, nil);

		else

			host_session.posh = { jwk = cached };

			return false;

		end

	end

	local log = host_session.log or module._log;

	log("debug", "Session direction: %s", tostring(host_session.direction));

	local url = build_url { scheme = "https", host = target_host, path = "/.well-known/posh/xmpp-server.json" };

	log("debug", "Request POSH information for %s", tostring(target_host));

	local redirect_followed = false;

	local function cb (response, code)

		if code ~= 200 then

			log("debug", "No or invalid POSH response received");

			resume();

			return;

		end

		log("debug", "Received POSH response");

		local jwk = json.decode(response);

		if not jwk or type(jwk) ~= "table" then

			log("error", "POSH response is not valid JSON!\n%s", tostring(response));

			resume();

			return;

		end

		if type(jwk.url) == "string" then

			if redirect_followed then

				redirect_followed = true;

				http.request(jwk.url, nil, cb);

			else

				log("error", "POSH had invalid redirect:\n%s", tostring(response));

				resume();

				return;

			end

		end

		host_session.posh = { orig = response };

		jwk.expires = os.time() + tonumber(jwk.expires) or 3600;

		host_session.posh.jwk = jwk;

		cache:set(target_host, jwk);

		resume();

	end

	http.request(url, nil, cb);

	return true;

end

-- Do POSH authentication

module:hook("s2s-check-certificate", function (event)

	local session, cert = event.session, event.cert;

	local log = session.log or module._log;

	if session.cert_identity_status == "valid" then

		log("debug", "Not trying POSH because certificate is already valid");

		return;

	end

	log("info", "Trying POSH authentication.");

	local wait, done = async.waiter();

	if posh_lookup(session, done) then

		wait();

	end

	local posh = session.posh;

	local jwk = posh and posh.jwk;

	local fingerprints = jwk and jwk.fingerprints;

	if type(fingerprints) ~= "table" then

		log("debug", "No POSH authentication data available");

		return;

	end

	local cert_der = pem2der(cert:pem());

	local cert_hashes = {};

	for i = 1, #hash_order do

		cert_hashes[i] = base64.encode(hash_funcs[i](cert_der));

	end

	for i = 1, #fingerprints do

		local fp = fingerprints[i];

		for j = 1, #hash_order do

			local hash = fp[hash_order[j]];

			if cert_hashes[j] == hash then

				session.cert_chain_status = "valid";

				session.cert_identity_status = "valid";

				log("debug", "POSH authentication succeeded!");

				return true;

			elseif hash then

				-- Don't try weaker hashes

				break;

			end

		end

	end

	log("debug", "POSH authentication failed!");

end);

function module.command(arg)

	if not arg[1] then

		print("Usage: mod_s2s_auth_posh /path/to/cert.pem")

		return 1;

	end

	local jwkset = { fingerprints = { }; expires = 86400; }

	for i, cert_file in ipairs(arg) do

		local cert, err = io.open(cert_file);

		if not cert then

			io.stderr:write(err, "\n");

			return 1;

		end

		local cert_pem = cert:read("*a");

		local cert_der, typ = pem2der(cert_pem);

		if typ == "CERTIFICATE" then

			jwkset.fingerprints[i] = { ["sha-256"] = base64.encode(hashes.sha256(cert_der)); };

		elseif typ then

			io.stderr:write(cert_file, " contained a ", typ:lower(), ", was expecting a certificate\n");

			return 1;

		else

			io.stderr:write(cert_file, " did not contain a certificate in PEM format\n");

			return 1;

		end

	end

	print(json.encode(jwkset));

	return 0;

end