-- Token authentication
-- Copyright (C) 2021-present 8x8, Inc.

local basexx = require "basexx";
local have_async, async = pcall(require, "util.async");
local hex = require "util.hex";
local jwt = module:require "luajwtjitsi";
local jid = require "util.jid";
local json_safe = require "cjson.safe";
local path = require "util.paths";
local sha256 = require "util.hashes".sha256;
local main_util = module:require "util";
local ends_with = main_util.ends_with;
local http_get_with_retry = main_util.http_get_with_retry;
local extract_subdomain = main_util.extract_subdomain;
local starts_with = main_util.starts_with;
local table_shallow_copy = main_util.table_shallow_copy;
local cjson_safe  = require 'cjson.safe'
local timer = require "util.timer";
local async = require "util.async";
local inspect = require 'inspect';

local nr_retries = 3;
local ssl = require "ssl";

-- TODO: Figure out a less arbitrary default cache size.
local cacheSize = module:get_option_number("jwt_pubkey_cache_size", 128);

-- the cache for generated asap jwt tokens
local jwtKeyCache = require 'util.cache'.new(cacheSize);

local ASAPTTL_THRESHOLD = module:get_option_number('asap_ttl_threshold', 600);
local ASAPTTL = module:get_option_number('asap_ttl', 3600);
local ASAPIssuer = module:get_option_string('asap_issuer', 'jitsi');
local ASAPAudience = module:get_option_string('asap_audience', 'jitsi');
local ASAPKeyId = module:get_option_string('asap_key_id', 'jitsi');
local ASAPKeyPath = module:get_option_string('asap_key_path', '/etc/prosody/certs/asap.key');

local ASAPKey;
local f = io.open(ASAPKeyPath, 'r');

if f then
    ASAPKey = f:read('*all');
    f:close();
end

local Util = {}
Util.__index = Util

--- Constructs util class for token verifications.
-- Constructor that uses the passed module to extract all the
-- needed configurations.
-- If configuration is missing returns nil
-- @param module the module in which options to check for configs.
-- @return the new instance or nil
function Util.new(module)
    local self = setmetatable({}, Util)

    self.appId = module:get_option_string("app_id");
    self.appSecret = module:get_option_string("app_secret");
    self.asapKeyServer = module:get_option_string("asap_key_server");
    -- A URL that will return json file with a mapping between kids and public keys
    -- If the response Cache-Control header we will respect it and refresh it
    self.cacheKeysUrl = module:get_option_string("cache_keys_url");
    self.signatureAlgorithm = module:get_option_string("signature_algorithm");
    self.allowEmptyToken = module:get_option_boolean("allow_empty_token");

    self.cache = require"util.cache".new(cacheSize);

    --[[
        Multidomain can be supported in some deployments. In these deployments
        there is a virtual conference muc, which address contains the subdomain
        to use. Those deployments are accessible
        by URL https://domain/subdomain.
        Then the address of the room will be:
        roomName@conference.subdomain.domain. This is like a virtual address
        where there is only one muc configured by default with address:
        conference.domain and the actual presentation of the room in that muc
        component is [subdomain]roomName@conference.domain.
        These setups relay on configuration 'muc_domain_base' which holds
        the main domain and we use it to subtract subdomains from the
        virtual addresses.
        The following confgurations are for multidomain setups and domain name
        verification:
     --]]

    -- optional parameter for custom muc component prefix,
    -- defaults to "conference"
    self.muc_domain_prefix = module:get_option_string(
        "muc_mapper_domain_prefix", "conference");
    -- domain base, which is the main domain used in the deployment,
    -- the main VirtualHost for the deployment
    self.muc_domain_base = module:get_option_string("muc_mapper_domain_base");
    -- The "real" MUC domain that we are proxying to
    if self.muc_domain_base then
        self.muc_domain = module:get_option_string(
            "muc_mapper_domain",
            self.muc_domain_prefix.."."..self.muc_domain_base);
    end
    -- whether domain name verification is enabled, by default it is enabled
    -- when disabled checking domain name and tenant if available will be skipped, we will check only room name.
    self.enableDomainVerification = module:get_option_boolean('enable_domain_verification', true);

    if self.allowEmptyToken == true then
        module:log("warn", "WARNING - empty tokens allowed");
    end

    if self.appId == nil then
        module:log("error", "'app_id' must not be empty");
        return nil;
    end

    if self.appSecret == nil and self.asapKeyServer == nil then
        module:log("error", "'app_secret' or 'asap_key_server' must be specified");
        return nil;
    end

    -- Set defaults for signature algorithm
    if self.signatureAlgorithm == nil then
        if self.asapKeyServer ~= nil then
            self.signatureAlgorithm = "RS256"
        elseif self.appSecret ~= nil then
            self.signatureAlgorithm = "HS256"
        end
    end

    --array of accepted issuers: by default only includes our appId
    self.acceptedIssuers = module:get_option_array('asap_accepted_issuers',{self.appId})

    --array of accepted audiences: by default only includes our appId
    self.acceptedAudiences = module:get_option_array('asap_accepted_audiences',{'*'})

    self.requireRoomClaim = module:get_option_boolean('asap_require_room_claim', true);

    if self.asapKeyServer and not have_async then
        module:log("error", "requires a version of Prosody with util.async");
        return nil;
    end

    if self.cacheKeysUrl then
        self.cachedKeys = {};
        local update_keys_cache;
        update_keys_cache = async.runner(function (name)
            local content, code, cache_for;
            content, code, cache_for = http_get_with_retry(self.cacheKeysUrl, nr_retries);
            if content ~= nil then
                local keys_to_delete = table_shallow_copy(self.cachedKeys);
                -- Let's convert any certificate to public key
                for k, v in pairs(cjson_safe.decode(content)) do
                    if starts_with(v, '-----BEGIN CERTIFICATE-----') then
                        self.cachedKeys[k] = ssl.loadcertificate(v):pubkey();
                        -- do not clean this key if it already exists
                        keys_to_delete[k] = nil;
                    end
                end
                -- let's schedule the clean in an hour and a half, current tokens will be valid for an hour
                timer.add_task(90*60, function ()
                    for k, _ in pairs(keys_to_delete) do
                        self.cachedKeys[k] = nil;
                    end
                end);

                if cache_for then
                    cache_for = tonumber(cache_for);
                    -- let's schedule new update 60 seconds before the cache expiring
                    if cache_for > 60 then
                        cache_for = cache_for - 60;
                    end
                    timer.add_task(cache_for, function ()
                        update_keys_cache:run("update_keys_cache");
                    end);
                else
                    -- no cache header let's consider updating in 6hours
                    timer.add_task(6*60*60, function ()
                        update_keys_cache:run("update_keys_cache");
                    end);
                end
            else
                module:log('warn', 'Failed to retrieve cached public keys code:%s', code);
                -- failed let's retry in 30 seconds
                timer.add_task(30, function ()
                    update_keys_cache:run("update_keys_cache");
                end);
            end
        end);
        update_keys_cache:run("update_keys_cache");
    end

    return self
end

function Util:set_asap_key_server(asapKeyServer)
    self.asapKeyServer = asapKeyServer;
end

function Util:set_asap_accepted_issuers(acceptedIssuers)
    self.acceptedIssuers = acceptedIssuers;
end

function Util:set_asap_accepted_audiences(acceptedAudiences)
    self.acceptedAudiences = acceptedAudiences;
end

function Util:set_asap_require_room_claim(checkRoom)
    self.requireRoomClaim = checkRoom;
end

function Util:clear_asap_cache()
    self.cache = require"util.cache".new(cacheSize);
end

--- Returns the public key by keyID
-- @param keyId the key ID to request
-- @return the public key (the content of requested resource) or nil
function Util:get_public_key(keyId)
    local content = self.cache:get(keyId);
    local code;
    if content == nil then
        -- If the key is not found in the cache.
        -- module:log("debug", "Cache miss for key: %s", keyId);
        local keyurl = path.join(self.asapKeyServer, hex.to(sha256(keyId))..'.pem');
        -- module:log("debug", "Fetching public key from: %s", keyurl);
        content, code = http_get_with_retry(keyurl, nr_retries);
        if content ~= nil then
            self.cache:set(keyId, content);
        else
            if code == nil then
                -- this is timout after nr_retries retries
                module:log('warn', 'Timeout retrieving %s from %s', keyId, keyurl);
            end
        end
        return content;
    else
        -- If the key is in the cache, use it.
        -- module:log("debug", "Cache hit for key: %s", keyId);
        return content;
    end
end

--- Verifies token and process needed values to be stored in the session.
-- Token is obtained from session.auth_token.
-- Stores in session the following values:
-- session.jitsi_meet_room - the room name value from the token
-- session.jitsi_meet_domain - the domain name value from the token
-- session.jitsi_meet_context_user - the user details from the token
-- session.jitsi_meet_context_room - the room details from the token
-- session.jitsi_meet_context_group - the group value from the token
-- session.jitsi_meet_context_features - the features value from the token
-- @param session the current session
-- @return false and error
function Util:process_and_verify_token(session)
    if session.auth_token == nil then
        if self.allowEmptyToken then
            return true;
        else
            return false, "not-allowed", "token required";
        end
    end

    local key;
    if session.public_key then
        -- We're using an public key stored in the session
        -- module:log("debug","Public key was found on the session");
        key = session.public_key;
    elseif self.asapKeyServer and session.auth_token ~= nil then
        -- We're fetching an public key from an ASAP server
        local dotFirst = session.auth_token:find("%.");
        if not dotFirst then return false, "not-allowed", "Invalid token" end
        local header, err = json_safe.decode(basexx.from_url64(session.auth_token:sub(1,dotFirst-1)));
        if err then
            return false, "not-allowed", "bad token format";
        end
        local kid = header["kid"];
        if kid == nil then
            return false, "not-allowed", "'kid' claim is missing";
        end
        local alg = header["alg"];
        if alg == nil then
            return false, "not-allowed", "'alg' claim is missing";
        end
        if alg.sub(alg,1,2) ~= "RS" then
            return false, "not-allowed", "'kid' claim only support with RS family";
        end

        if self.cachedKeys and self.cachedKeys[kid] then
            key = self.cachedKeys[kid];
        else
            key = self:get_public_key(kid);
        end

        if key == nil then
            return false, "not-allowed", "could not obtain public key";
        end
    elseif self.appSecret ~= nil then
        -- We're using a symmetric secret
        key = self.appSecret
    end

    if key == nil then
        return false, "not-allowed", "signature verification key is missing";
    end

    -- now verify the whole token
    local claims, msg = jwt.verify(
        session.auth_token,
        self.signatureAlgorithm,
        key,
        self.acceptedIssuers,
        self.acceptedAudiences
    )
    if claims ~= nil then
        if self.requireRoomClaim then
            local roomClaim = claims["room"];
            if roomClaim == nil then
                return false, "'room' claim is missing";
            end
        end

        -- Binds room name to the session which is later checked on MUC join
        session.jitsi_meet_room = claims["room"];
        -- Binds domain name to the session
        session.jitsi_meet_domain = claims["sub"];

        -- Binds the user details to the session if available
        if claims["context"] ~= nil then
          session.jitsi_meet_str_tenant = claims["context"]["tenant"];

          if claims["context"]["user"] ~= nil then
            session.jitsi_meet_context_user = claims["context"]["user"];
          end

          if claims["context"]["group"] ~= nil then
            -- Binds any group details to the session
            session.jitsi_meet_context_group = claims["context"]["group"];
          end

          if claims["context"]["features"] ~= nil then
            -- Binds any features details to the session
            session.jitsi_meet_context_features = claims["context"]["features"];
          end
          if claims["context"]["room"] ~= nil then
            session.jitsi_meet_context_room = claims["context"]["room"]
          end
        elseif claims["user_id"] then
          session.jitsi_meet_context_user = {};
          session.jitsi_meet_context_user.id = claims["user_id"];
        end

        -- fire event that token has been verified and pass the session and the decoded token
        prosody.events.fire_event('jitsi-authentication-token-verified', {
            session = session;
            claims = claims;
        });

        if session.contextRequired and claims["context"] == nil then
            return false, "not-allowed", 'jwt missing required context claim';
        end

        return true;
    else
        return false, "not-allowed", msg;
    end
end

--- Verifies room name and domain if necessary.
-- Checks configs and if necessary checks the room name extracted from
-- room_address against the one saved in the session when token was verified.
-- Also verifies domain name from token against the domain in the room_address,
-- if enableDomainVerification is enabled.
-- @param session the current session
-- @param room_address the whole room address as received
-- @return returns true in case room was verified or there is no need to verify
--         it and returns false in case verification was processed
--         and was not successful
function Util:verify_room(session, room_address)
    if self.allowEmptyToken and session.auth_token == nil then
        --module:log("debug", "Skipped room token verification - empty tokens are allowed");
        return true;
    end

    -- extract room name using all chars, except the not allowed ones
    local room,_,_ = jid.split(room_address);
    if room == nil then
        log("error",
            "Unable to get name of the MUC room ? to: %s", room_address);
        return true;
    end

    local auth_room = session.jitsi_meet_room;
    if auth_room then
        if type(auth_room) == 'string' then
            auth_room = string.lower(auth_room);
        else
            module:log('warn', 'session.jitsi_meet_room not string: %s', inspect(auth_room));
        end
    end
    if not self.enableDomainVerification then
        -- if auth_room is missing, this means user is anonymous (no token for
        -- its domain) we let it through, jicofo is verifying creation domain
        if auth_room and (room ~= auth_room and not ends_with(room, ']'..auth_room)) and auth_room ~= '*' then
            return false;
        end

        return true;
    end

    local room_address_to_verify = jid.bare(room_address);
    local room_node = jid.node(room_address);
    -- parses bare room address, for multidomain expected format is:
    -- [subdomain]roomName@conference.domain
    local target_subdomain, target_room = extract_subdomain(room_node);

    -- if we have '*' as room name in token, this means all rooms are allowed
    -- so we will use the actual name of the room when constructing strings
    -- to verify subdomains and domains to simplify checks
    local room_to_check;
    if auth_room == '*' then
        -- authorized for accessing any room assign to room_to_check the actual
        -- room name
        if target_room ~= nil then
            -- we are in multidomain mode and we were able to extract room name
            room_to_check = target_room;
        else
            -- no target_room, room_address_to_verify does not contain subdomain
            -- so we get just the node which is the room name
            room_to_check = room_node;
        end
    else
        -- no wildcard, so check room against authorized room from the token
        if session.jitsi_meet_context_room and (session.jitsi_meet_context_room["regex"] == true or session.jitsi_meet_context_room["regex"] == "true") then
            if target_room ~= nil then
                -- room with subdomain
                room_to_check = target_room:match(auth_room);
            else
                room_to_check = room_node:match(auth_room);
            end
        else
            -- not a regex
            room_to_check = auth_room;
        end
        -- module:log("debug", "room to check: %s", room_to_check)
        if not room_to_check then
            if not self.requireRoomClaim then
                -- if we do not require to have the room claim, and it is missing
                -- there is no point of continue and verifying the roomName and the tenant
                return true;
            end

            return false;
        end
    end

    if session.jitsi_meet_str_tenant
        and string.lower(session.jitsi_meet_str_tenant) ~= session.jitsi_web_query_prefix then
        module:log('warn', 'Tenant differs for user:%s group:%s url_tenant:%s token_tenant:%s',
            session.jitsi_meet_context_user and session.jitsi_meet_context_user.id or '',
            session.jitsi_meet_context_group,
            session.jitsi_web_query_prefix, session.jitsi_meet_str_tenant);
        session.jitsi_meet_tenant_mismatch = true;
    end

    local auth_domain = string.lower(session.jitsi_meet_domain);
    local subdomain_to_check;
    if target_subdomain then
        if auth_domain == '*' then
            -- check for wildcard in JWT claim, allow access if found
            subdomain_to_check = target_subdomain;
        else
            -- no wildcard in JWT claim, so check subdomain against sub in token
            subdomain_to_check = auth_domain;
        end
        -- from this point we depend on muc_domain_base,
        -- deny access if option is missing
        if not self.muc_domain_base then
            module:log("warn", "No 'muc_domain_base' option set, denying access!");
            return false;
        end

        return room_address_to_verify == jid.join(
            "["..subdomain_to_check.."]"..room_to_check, self.muc_domain);
    else
        if auth_domain == '*' then
            -- check for wildcard in JWT claim, allow access if found
            subdomain_to_check = self.muc_domain;
        else
            -- no wildcard in JWT claim, so check subdomain against sub in token
            subdomain_to_check = self.muc_domain_prefix.."."..auth_domain;
        end
        -- we do not have a domain part (multidomain is not enabled)
        -- verify with info from the token
        return room_address_to_verify == jid.join(room_to_check, subdomain_to_check);
    end
end

function Util:generateAsapToken(audience)
    if not ASAPKey then
        module:log('warn', 'No ASAP Key read, asap key generation is disabled');
        return ''
    end

    audience = audience or ASAPAudience
    local t = os.time()
    local err
    local exp_key = 'asap_exp.'..audience
    local token_key = 'asap_token.'..audience
    local exp = jwtKeyCache:get(exp_key)
    local token = jwtKeyCache:get(token_key)

    --if we find a token and it isn't too far from expiry, then use it
    if token ~= nil and exp ~= nil then
        exp = tonumber(exp)
        if (exp - t) > ASAPTTL_THRESHOLD then
            return token
        end
    end

    --expiry is the current time plus TTL
    exp = t + ASAPTTL
    local payload = {
        iss = ASAPIssuer,
        aud = audience,
        nbf = t,
        exp = exp,
    }

    -- encode
    local alg = 'RS256'
    token, err = jwt.encode(payload, ASAPKey, alg, { kid = ASAPKeyId })
    if not err then
        token = 'Bearer '..token
        jwtKeyCache:set(exp_key, exp)
        jwtKeyCache:set(token_key, token)
        return token
    else
        return ''
    end
end

return Util;
