auth-filters: add simple file-based authentication scheme

[ps-cgit] / filters / file-authentication.lua

-- This script may be used with the auth-filter.
--
-- Requirements:
--      luacrypto >= 0.3
--      <http://mkottman.github.io/luacrypto/>
--      luaposix
--      <https://github.com/luaposix/luaposix>
--
local sysstat = require("posix.sys.stat")
local unistd = require("posix.unistd")
local crypto = require("crypto")


-- This file should contain a series of lines in the form of:
--      username1:hash1
--      username2:hash2
--      username3:hash3
--      ...
-- Hashes can be generated using something like `mkpasswd -m sha-512 -R 300000`.
-- This file should not be world-readable.
local users_filename = "/etc/cgit-auth/users"

-- This file should contain a series of lines in the form of:
--      groupname1:username1,username2,username3,...
--      ...
local groups_filename = "/etc/cgit-auth/groups"

-- This file should contain a series of lines in the form of:
--      reponame1:groupname1,groupname2,groupname3,...
--      ...
local repos_filename = "/etc/cgit-auth/repos"

-- Set this to a path this script can write to for storing a persistent
-- cookie secret, which should not be world-readable.
local secret_filename = "/var/cache/cgit/auth-secret"

--
--
-- Authentication functions follow below. Swap these out if you want different authentication semantics.
--
--

-- Looks up a hash for a given user.
function lookup_hash(user)
        local line
        for line in io.lines(users_filename) do
                local u, h = string.match(line, "(.-):(.+)")
                if u:lower() == user:lower() then
                        return h
                end
        end
        return nil
end

-- Looks up users for a given repo.
function lookup_users(repo)
        local users = nil
        local groups = nil
        local line, group, user
        for line in io.lines(repos_filename) do
                local r, g = string.match(line, "(.-):(.+)")
                if r == repo then
                        groups = { }
                        for group in string.gmatch(g, "([^,]+)") do
                                groups[group:lower()] = true
                        end
                        break
                end
        end
        if groups == nil then
                return nil
        end
        for line in io.lines(groups_filename) do
                local g, u = string.match(line, "(.-):(.+)")
                if groups[g:lower()] then
                        if users == nil then
                                users = { }
                        end
                        for user in string.gmatch(u, "([^,]+)") do
                                users[user:lower()] = true
                        end
                end
        end
        return users
end


-- Sets HTTP cookie headers based on post and sets up redirection.
function authenticate_post()
        local hash = lookup_hash(post["username"])
        local redirect = validate_value("redirect", post["redirect"])

        if redirect == nil then
                not_found()
                return 0
        end

        redirect_to(redirect)

        if hash == nil or hash ~= unistd.crypt(post["password"], hash) then
                set_cookie("cgitauth", "")
        else
                -- One week expiration time
                local username = secure_value("username", post["username"], os.time() + 604800)
                set_cookie("cgitauth", username)
        end

        html("\n")
        return 0
end


-- Returns 1 if the cookie is valid and 0 if it is not.
function authenticate_cookie()
        accepted_users = lookup_users(cgit["repo"])
        if accepted_users == nil then
                -- We return as valid if the repo is not protected.
                return 1
        end

        local username = validate_value("username", get_cookie(http["cookie"], "cgitauth"))
        if username == nil or not accepted_users[username:lower()] then
                return 0
        else
                return 1
        end
end

-- Prints the html for the login form.
function body()
        html("<h2>Authentication Required</h2>")
        html("<form method='post' action='")
        html_attr(cgit["login"])
        html("'>")
        html("<input type='hidden' name='redirect' value='")
        html_attr(secure_value("redirect", cgit["url"], 0))
        html("' />")
        html("<table>")
        html("<tr><td><label for='username'>Username:</label></td><td><input id='username' name='username' autofocus /></td></tr>")
        html("<tr><td><label for='password'>Password:</label></td><td><input id='password' name='password' type='password' /></td></tr>")
        html("<tr><td colspan='2'><input value='Login' type='submit' /></td></tr>")
        html("</table></form>")

        return 0
end



--
--
-- Wrapper around filter API, exposing the http table, the cgit table, and the post table to the above functions.
--
--

local actions = {}
actions["authenticate-post"] = authenticate_post
actions["authenticate-cookie"] = authenticate_cookie
actions["body"] = body

function filter_open(...)
        action = actions[select(1, ...)]

        http = {}
        http["cookie"] = select(2, ...)
        http["method"] = select(3, ...)
        http["query"] = select(4, ...)
        http["referer"] = select(5, ...)
        http["path"] = select(6, ...)
        http["host"] = select(7, ...)
        http["https"] = select(8, ...)

        cgit = {}
        cgit["repo"] = select(9, ...)
        cgit["page"] = select(10, ...)
        cgit["url"] = select(11, ...)
        cgit["login"] = select(12, ...)

end

function filter_close()
        return action()
end

function filter_write(str)
        post = parse_qs(str)
end


--
--
-- Utility functions based on keplerproject/wsapi.
--
--

function url_decode(str)
        if not str then
                return ""
        end
        str = string.gsub(str, "+", " ")
        str = string.gsub(str, "%%(%x%x)", function(h) return string.char(tonumber(h, 16)) end)
        str = string.gsub(str, "\r\n", "\n")
        return str
end

function url_encode(str)
        if not str then
                return ""
        end
        str = string.gsub(str, "\n", "\r\n")
        str = string.gsub(str, "([^%w ])", function(c) return string.format("%%%02X", string.byte(c)) end)
        str = string.gsub(str, " ", "+")
        return str
end

function parse_qs(qs)
        local tab = {}
        for key, val in string.gmatch(qs, "([^&=]+)=([^&=]*)&?") do
                tab[url_decode(key)] = url_decode(val)
        end
        return tab
end

function get_cookie(cookies, name)
        cookies = string.gsub(";" .. cookies .. ";", "%s*;%s*", ";")
        return url_decode(string.match(cookies, ";" .. name .. "=(.-);"))
end


--
--
-- Cookie construction and validation helpers.
--
--

local secret = nil

-- Loads a secret from a file, creates a secret, or returns one from memory.
function get_secret()
        if secret ~= nil then
                return secret
        end
        local secret_file = io.open(secret_filename, "r")
        if secret_file == nil then
                local old_umask = sysstat.umask(63)
                local temporary_filename = secret_filename .. ".tmp." .. crypto.hex(crypto.rand.bytes(16))
                local temporary_file = io.open(temporary_filename, "w")
                if temporary_file == nil then
                        os.exit(177)
                end
                temporary_file:write(crypto.hex(crypto.rand.bytes(32)))
                temporary_file:close()
                unistd.link(temporary_filename, secret_filename) -- Intentionally fails in the case that another process is doing the same.
                unistd.unlink(temporary_filename)
                sysstat.umask(old_umask)
                secret_file = io.open(secret_filename, "r")
        end
        if secret_file == nil then
                os.exit(177)
        end
        secret = secret_file:read()
        secret_file:close()
        if secret:len() ~= 64 then
                os.exit(177)
        end
        return secret
end

-- Returns value of cookie if cookie is valid. Otherwise returns nil.
function validate_value(expected_field, cookie)
        local i = 0
        local value = ""
        local field = ""
        local expiration = 0
        local salt = ""
        local hmac = ""

        if cookie == nil or cookie:len() < 3 or cookie:sub(1, 1) == "|" then
                return nil
        end

        for component in string.gmatch(cookie, "[^|]+") do
                if i == 0 then
                        field = component
                elseif i == 1 then
                        value = component
                elseif i == 2 then
                        expiration = tonumber(component)
                        if expiration == nil then
                                expiration = -1
                        end
                elseif i == 3 then
                        salt = component
                elseif i == 4 then
                        hmac = component
                else
                        break
                end
                i = i + 1
        end

        if hmac == nil or hmac:len() == 0 then
                return nil
        end

        -- Lua hashes strings, so these comparisons are time invariant.
        if hmac ~= crypto.hmac.digest("sha256", field .. "|" .. value .. "|" .. tostring(expiration) .. "|" .. salt, get_secret()) then
                return nil
        end

        if expiration == -1 or (expiration ~= 0 and expiration <= os.time()) then
                return nil
        end

        if url_decode(field) ~= expected_field then
                return nil
        end

        return url_decode(value)
end

function secure_value(field, value, expiration)
        if value == nil or value:len() <= 0 then
                return ""
        end

        local authstr = ""
        local salt = crypto.hex(crypto.rand.bytes(16))
        value = url_encode(value)
        field = url_encode(field)
        authstr = field .. "|" .. value .. "|" .. tostring(expiration) .. "|" .. salt
        authstr = authstr .. "|" .. crypto.hmac.digest("sha256", authstr, get_secret())
        return authstr
end

function set_cookie(cookie, value)
        html("Set-Cookie: " .. cookie .. "=" .. value .. "; HttpOnly")
        if http["https"] == "yes" or http["https"] == "on" or http["https"] == "1" then
                html("; secure")
        end
        html("\n")
end

function redirect_to(url)
        html("Status: 302 Redirect\n")
        html("Cache-Control: no-cache, no-store\n")
        html("Location: " .. url .. "\n")
end

function not_found()
        html("Status: 404 Not Found\n")
        html("Cache-Control: no-cache, no-store\n\n")
end