-- sasl.lua v0.4
-- Copyright (C) 2008-2010 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 s_match = string.match;
local type = type
local base64 = require "util.encodings".base64;
local hashes = require "util.hashes";
local generate_uuid = require "util.uuid".generate;
local saslprep = require "util.encodings".stringprep.saslprep;
local nodeprep = require "util.encodings".stringprep.nodeprep;
local log = require "util.logger".init("sasl");
local	binaryXOR = require "util.strbitop".sxor;

local _ENV = nil;
-- luacheck: std none

--=========================
--SASL SCRAM-SHA-1 according to RFC 5802

--[[
Supported Authentication Backends

scram_{MECH}:
	-- MECH being a standard hash name (like those at IANA's hash registry) with '-' replaced with '_'
	function(username, realm)
		return stored_key, server_key, iteration_count, salt, state;
	end

Supported Channel Binding Backends

'tls-unique' according to RFC 5929
]]

local default_i = 10000

local function validate_username(username, _nodeprep)
	-- check for forbidden char sequences
	for eq in username:gmatch("=(.?.?)") do
		if eq ~= "2C" and eq ~= "3D" then
			return false
		end
	end

	-- replace =2C with , and =3D with =
	username = username:gsub("=2C", ",");
	username = username:gsub("=3D", "=");

	-- apply SASLprep
	username = saslprep(username);

	if username and _nodeprep ~= false then
		username = (_nodeprep or nodeprep)(username);
	end

	return username and #username>0 and username;
end

local function hashprep(hashname)
	return hashname:lower():gsub("-", "_");
end

local function get_scram_hasher(H, HMAC, Hi)
	return function (password, salt, iteration_count)
		if type(password) ~= "string" or type(salt) ~= "string" or type(iteration_count) ~= "number" then
			return false, "inappropriate argument types"
		end
		if iteration_count < 4096 then
			log("warn", "Iteration count < 4096 which is the suggested minimum according to RFC 5802.")
		end
		password = saslprep(password);
		if not password then
			return false, "password fails SASLprep";
		end
		local salted_password = Hi(password, salt, iteration_count);
		local stored_key = H(HMAC(salted_password, "Client Key"))
		local server_key = HMAC(salted_password, "Server Key");
		return true, stored_key, server_key
	end
end

local function scram_gen(hash_name, H_f, HMAC_f, get_auth_db, expect_cb)
	local profile_name = "scram_" .. hashprep(hash_name);
	local function scram_hash(self, message)
		local support_channel_binding = false;
		if self.profile.cb then support_channel_binding = true; end

		if type(message) ~= "string" or #message == 0 then return "failure", "malformed-request" end
		local state = self.state;
		if not state then
			-- we are processing client_first_message
			local client_first_message = message;

			-- TODO: fail if authzid is provided, since we don't support them yet
			-- luacheck: ignore 211/authzid
			local gs2_header, gs2_cbind_flag, gs2_cbind_name, authzid, client_first_message_bare, username, clientnonce
				= s_match(client_first_message, "^(([pny])=?([^,]*),([^,]*),)(m?=?[^,]*,?n=([^,]*),r=([^,]*),?.*)$");

			if not gs2_cbind_flag then
				return "failure", "malformed-request";
			end

			if support_channel_binding and gs2_cbind_flag == "y" then
				-- "y" -> client does support channel binding
				--        but thinks the server does not.
					return "failure", "malformed-request";
				end

			if gs2_cbind_flag == "n" then
				-- "n" -> client doesn't support channel binding.
				if expect_cb then
					log("debug", "Client unexpectedly doesn't support channel binding");
					-- XXX Is it sensible to abort if the client starts -PLUS but doesn't use channel binding?
				end
				support_channel_binding = false;
			end

			if support_channel_binding and gs2_cbind_flag == "p" then
				-- check whether we support the proposed channel binding type
				if not self.profile.cb[gs2_cbind_name] then
					return "failure", "malformed-request", "Proposed channel binding type isn't supported.";
				end
			else
				-- no channel binding,
				gs2_cbind_name = nil;
			end

			username = validate_username(username, self.profile.nodeprep);
			if not username then
				log("debug", "Username violates either SASLprep or contains forbidden character sequences.")
				return "failure", "malformed-request", "Invalid username.";
			end
			self.username = username;

			-- retrieve credentials
			local stored_key, server_key, salt, iteration_count;
			if self.profile.plain then
				local password, status = self.profile.plain(self, username, self.realm)
				if status == nil then return "failure", "not-authorized"
				elseif status == false then return "failure", "account-disabled" end

				password = saslprep(password);
				if not password then
					log("debug", "Password violates SASLprep.");
					return "failure", "not-authorized", "Invalid password."
				end

				salt = generate_uuid();
				iteration_count = default_i;

				local succ;
				succ, stored_key, server_key = get_auth_db(password, salt, iteration_count);
				if not succ then
					log("error", "Generating authentication database failed. Reason: %s", stored_key);
					return "failure", "temporary-auth-failure";
				end
			elseif self.profile[profile_name] then
				local status;
				stored_key, server_key, iteration_count, salt, status = self.profile[profile_name](self, username, self.realm);
				if status == nil then return "failure", "not-authorized"
				elseif status == false then return "failure", "account-disabled" end
			end

			local nonce = clientnonce .. generate_uuid();
			local server_first_message = ("r=%s,s=%s,i=%d"):format(nonce, base64.encode(salt), iteration_count);
			self.state = {
				gs2_header = gs2_header;
				gs2_cbind_name = gs2_cbind_name;
				username = self.username; -- Reference property instead of local, in case it was modified by the profile
				nonce = nonce;

				server_key = server_key;
				stored_key = stored_key;
				client_first_message_bare = client_first_message_bare;
				server_first_message = server_first_message;
			}
			return "challenge", server_first_message
		else
			-- we are processing client_final_message
			local client_final_message = message;

			local client_final_message_without_proof, channelbinding, nonce, proof
				= s_match(client_final_message, "(c=([^,]*),r=([^,]*),?.-),p=(.*)$");

			if not proof or not nonce or not channelbinding then
				return "failure", "malformed-request", "Missing an attribute(p, r or c) in SASL message.";
			end

			local client_gs2_header = base64.decode(channelbinding)
			local our_client_gs2_header = state["gs2_header"]
			if state.gs2_cbind_name then
				-- we support channelbinding, so check if the value is valid
				our_client_gs2_header = our_client_gs2_header .. self.profile.cb[state.gs2_cbind_name](self);
			end
			if client_gs2_header ~= our_client_gs2_header then
				return "failure", "malformed-request", "Invalid channel binding value.";
			end

			if nonce ~= state.nonce then
				return "failure", "malformed-request", "Wrong nonce in client-final-message.";
			end

			local ServerKey = state.server_key;
			local StoredKey = state.stored_key;

			local AuthMessage = state.client_first_message_bare .. "," .. state.server_first_message .. "," .. client_final_message_without_proof
			local ClientSignature = HMAC_f(StoredKey, AuthMessage)
			local ClientKey = binaryXOR(ClientSignature, base64.decode(proof))
			local ServerSignature = HMAC_f(ServerKey, AuthMessage)

			if StoredKey == H_f(ClientKey) then
				local server_final_message = "v="..base64.encode(ServerSignature);
				return "success", server_final_message;
			else
				return "failure", "not-authorized", "The response provided by the client doesn't match the one we calculated.";
			end
		end
	end
	return scram_hash;
end

local auth_db_getters = {}
local function init(registerMechanism)
	local function registerSCRAMMechanism(hash_name, hash, hmac_hash, pbkdf2)
		local get_auth_db = get_scram_hasher(hash, hmac_hash, pbkdf2);
		auth_db_getters[hash_name] = get_auth_db;
		registerMechanism("SCRAM-"..hash_name,
			{"plain", "scram_"..(hashprep(hash_name))},
			scram_gen(hash_name:lower(), hash, hmac_hash, get_auth_db));

		-- register channel binding equivalent
		registerMechanism("SCRAM-"..hash_name.."-PLUS",
			{"plain", "scram_"..(hashprep(hash_name))},
			scram_gen(hash_name:lower(), hash, hmac_hash, get_auth_db, true), {"tls-unique"});
	end

	registerSCRAMMechanism("SHA-1", hashes.sha1, hashes.hmac_sha1, hashes.pbkdf2_hmac_sha1);
	registerSCRAMMechanism("SHA-256", hashes.sha256, hashes.hmac_sha256, hashes.pbkdf2_hmac_sha256);
end

return {
	get_hash = get_scram_hasher;
	hashers = auth_db_getters;
	getAuthenticationDatabaseSHA1 = get_scram_hasher(hashes.sha1, hashes.hmac_sha1, hashes.pbkdf2_hmac_sha1); -- COMPAT
	init = init;
}
