-- sasl.lua v0.4

-- Copyright (C) 2008-2009 Tobias Markmann

--

--    All rights reserved.

--

--    Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

--

--        * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

--        * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

--        * Neither the name of Tobias Markmann nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

--

--    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

local md5 = require "util.hashes".md5;

local log = require "util.logger".init("sasl");

local tostring = tostring;

local st = require "util.stanza";

local generate_uuid = require "util.uuid".generate;

local t_insert, t_concat = table.insert, table.concat;

local to_byte, to_char = string.byte, string.char;

local to_unicode = require "util.encodings".idna.to_unicode;

local s_match = string.match;

local gmatch = string.gmatch

local string = string

local math = require "math"

local type = type

local error = error

local print = print

module "sasl"

-- Credentials handler:

--   Arguments: ("PLAIN", user, host, password)

--   Returns: true (success) | false (fail) | nil (user unknown)

local function new_plain(realm, credentials_handler)

	local object = { mechanism = "PLAIN", realm = realm, credentials_handler = credentials_handler}

	function object.feed(self, message)

		if message == "" or message == nil then return "failure", "malformed-request" end

		local response = message

		local authorization = s_match(response, "([^%z]+)")

		local authentication = s_match(response, "%z([^%z]+)%z")

		local password = s_match(response, "%z[^%z]+%z([^%z]+)")

    if authentication == nil or password == nil then return "failure", "malformed-request" end

    self.username = authentication

    local auth_success = self.credentials_handler("PLAIN", self.username, self.realm, password)

    if auth_success then

      return "success"

    elseif auth_success == nil then

      return "failure", "account-disabled"

    else

      return "failure", "not-authorized"

    end

  end

  return object

end

-- credentials_handler:

--   Arguments: (mechanism, node, domain, realm, decoder)

--   Returns: Password encoding, (plaintext) password

-- implementing RFC 2831

local function new_digest_md5(realm, credentials_handler)

	--TODO complete support for authzid

	local function serialize(message)

		local data = ""

		if type(message) ~= "table" then error("serialize needs an argument of type table.") end

		-- testing all possible values

		if message["realm"] then data = data..[[realm="]]..message.realm..[[",]] end

		if message["nonce"] then data = data..[[nonce="]]..message.nonce..[[",]] end

		if message["qop"] then data = data..[[qop="]]..message.qop..[[",]] end

		if message["charset"] then data = data..[[charset=]]..message.charset.."," end

		if message["algorithm"] then data = data..[[algorithm=]]..message.algorithm.."," end

		if message["rspauth"] then data = data..[[rspauth=]]..message.rspauth.."," end

		data = data:gsub(",$", "")

		return data

	end

	local function utf8tolatin1ifpossible(passwd)

		local i = 1;

		while i <= #passwd do

			local passwd_i = to_byte(passwd:sub(i, i));

			if passwd_i > 0x7F then

				if passwd_i < 0xC0 or passwd_i > 0xC3 then

					return passwd;

				end

				i = i + 1;

				passwd_i = to_byte(passwd:sub(i, i));

				if passwd_i < 0x80 or passwd_i > 0xBF then

					return passwd;

				end

			end

			i = i + 1;

		end

		local p = {};

		local j = 0;

		i = 1;

		while (i <= #passwd) do

			local passwd_i = to_byte(passwd:sub(i, i));

			if passwd_i > 0x7F then

				i = i + 1;

				local passwd_i_1 = to_byte(passwd:sub(i, i));

				t_insert(p, to_char(passwd_i%4*64 + passwd_i_1%64)); -- I'm so clever

			else

				t_insert(p, to_char(passwd_i));

			end

			i = i + 1;

		end

		return t_concat(p);

	end

	local function latin1toutf8(str)

		local p = {};

		for ch in gmatch(str, ".") do

			ch = to_byte(ch);

			if (ch < 0x80) then

				t_insert(p, to_char(ch));

			elseif (ch < 0xC0) then

				t_insert(p, to_char(0xC2, ch));

			else

				t_insert(p, to_char(0xC3, ch - 64));

			end

		end

		return t_concat(p);

	end

	local function parse(data)

		local message = {}

		for k, v in gmatch(data, [[([%w%-]+)="?([^",%z]*)"?,?]]) do -- FIXME The hacky regex makes me shudder

			message[k] = v;

		end

		return message;

	end

	local object = { mechanism = "DIGEST-MD5", realm = realm, credentials_handler = credentials_handler};

	object.nonce = generate_uuid();

	object.step = 0;

	object.nonce_count = {};

	function object.feed(self, message)

		self.step = self.step + 1;

		if (self.step == 1) then

			local challenge = serialize({	nonce = object.nonce,

											qop = "auth",

											charset = "utf-8",

											algorithm = "md5-sess",

											realm = self.realm});

			return "challenge", challenge;

		elseif (self.step == 2) then

			local response = parse(message);

			-- check for replay attack

			if response["nc"] then

				if self.nonce_count[response["nc"]] then return "failure", "not-authorized" end

			end

			-- check for username, it's REQUIRED by RFC 2831

			if not response["username"] then

				return "failure", "malformed-request";

			end

			self["username"] = response["username"];

			-- check for nonce, ...

			if not response["nonce"] then

				return "failure", "malformed-request";

			else

				-- check if it's the right nonce

				if response["nonce"] ~= tostring(self.nonce) then return "failure", "malformed-request" end

			end

			if not response["cnonce"] then return "failure", "malformed-request", "Missing entry for cnonce in SASL message." end

			if not response["qop"] then response["qop"] = "auth" end

			if response["realm"] == nil or response["realm"] == "" then

				response["realm"] = "";

			elseif response["realm"] ~= self.realm then

				return "failure", "not-authorized", "Incorrect realm value";

			end

			local decoder;

			if response["charset"] == nil then

				decoder = utf8tolatin1ifpossible;

			elseif response["charset"] ~= "utf-8" then

				return "failure", "incorrect-encoding", "The client's response uses "..response["charset"].." for encoding with isn't supported by sasl.lua. Supported encodings are latin or utf-8.";

			end

			local domain = "";

			local protocol = "";

			if response["digest-uri"] then

				protocol, domain = response["digest-uri"]:match("(%w+)/(.*)$");

				if protocol == nil or domain == nil then return "failure", "malformed-request" end

			else

				return "failure", "malformed-request", "Missing entry for digest-uri in SASL message."

			end

			--TODO maybe realm support

			self.username = response["username"];

			local password_encoding, Y = self.credentials_handler("DIGEST-MD5", response["username"], self.realm, response["realm"], decoder);

			if Y == nil then return "failure", "not-authorized"

			elseif Y == false then return "failure", "account-disabled" end

			local A1 = "";

			if response.authzid then

				if response.authzid == self.username or response.authzid == self.username.."@"..self.realm then

					-- COMPAT

					log("warn", "Client is violating RFC 3920 (section 6.1, point 7).");

					A1 = Y..":"..response["nonce"]..":"..response["cnonce"]..":"..response.authzid;

				else

					return "failure", "invalid-authzid";

				end

			else

				A1 = Y..":"..response["nonce"]..":"..response["cnonce"];

			end

			local A2 = "AUTHENTICATE:"..protocol.."/"..domain;

			local HA1 = md5(A1, true);

			local HA2 = md5(A2, true);

			local KD = HA1..":"..response["nonce"]..":"..response["nc"]..":"..response["cnonce"]..":"..response["qop"]..":"..HA2;

			local response_value = md5(KD, true);

			if response_value == response["response"] then

				-- calculate rspauth

				A2 = ":"..protocol.."/"..domain;

				HA1 = md5(A1, true);

				HA2 = md5(A2, true);

				KD = HA1..":"..response["nonce"]..":"..response["nc"]..":"..response["cnonce"]..":"..response["qop"]..":"..HA2

				local rspauth = md5(KD, true);

				self.authenticated = true;

				return "challenge", serialize({rspauth = rspauth});

			else

				return "failure", "not-authorized", "The response provided by the client doesn't match the one we calculated."

			end

		elseif self.step == 3 then

			if self.authenticated ~= nil then return "success"

			else return "failure", "malformed-request" end

		end

	end

	return object;

end

-- Credentials handler: Can be nil. If specified, should take the mechanism as

-- the only argument, and return true for OK, or false for not-OK (TODO)

local function new_anonymous(realm, credentials_handler)

	local object = { mechanism = "ANONYMOUS", realm = realm, credentials_handler = credentials_handler}

		function object.feed(self, message)

			return "success"

		end

	object["username"] = generate_uuid()

	return object

end

function new(mechanism, realm, credentials_handler)

	local object

	if mechanism == "PLAIN" then object = new_plain(realm, credentials_handler)

	elseif mechanism == "DIGEST-MD5" then object = new_digest_md5(realm, credentials_handler)

	elseif mechanism == "ANONYMOUS" then object = new_anonymous(realm, credentials_handler)

	else

		log("debug", "Unsupported SASL mechanism: "..tostring(mechanism));

		return nil

	end

	return object

end

return _M;