HAProxy configuration and lua scripts implementing a challenge-response page where visitors solve a captcha and/or proof-of-work (cpu intensive) task. Intended to stop bots, spam, ddos, etc.
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_M = {}
local url = require("url")
local utils = require("utils")
local cookie = require("cookie")
local json = require("json")
local sha = require("sha")
local captcha_secret = os.getenv("HCAPTCHA_SECRET")
local captcha_sitekey = os.getenv("HCAPTCHA_SITEKEY")
local hcaptcha_cookie_secret = os.getenv("CAPTCHA_COOKIE_SECRET")
local pow_cookie_secret = os.getenv("POW_COOKIE_SECRET")
local ray_id = os.getenv("RAY_ID")
local captcha_provider_domain = "hcaptcha.com"
local captcha_map = Map.new("/etc/haproxy/ddos.map", Map._str);
function _M.setup_servers()
local backend_name = os.getenv("BACKEND_NAME")
local server_prefix = os.getenv("SERVER_PREFIX")
if backend_name == nil or server_prefix == nil then
return;
end
local hosts_map = Map.new("/etc/haproxy/hosts.map", Map._str);
local handle = io.open("/etc/haproxy/hosts.map", "r")
local line = handle:read("*line")
local counter = 1
while line do
local domain, backend_host = line:match("([^%s]+)%s+([^%s]+)")
local port_index = backend_host:match'^.*():'
local backend_hostname = backend_host:sub(0, port_index-1)
local backend_port = backend_host:sub(port_index + 1)
core.set_map("/etc/haproxy/backends.map", domain, server_prefix..counter)
local proxy = core.proxies[backend_name].servers[server_prefix..counter]
proxy:set_addr(backend_hostname, backend_port)
proxy:set_ready()
line = handle:read("*line")
counter = counter + 1
end
handle:close()
end
-- main page template
local body_template = [[
<!DOCTYPE html>
<html>
<head>
<meta name='viewport' content='width=device-width initial-scale=1'>
<title>Hold on...</title>
<style>
:root{--text-color:#c5c8c6;--bg-color:#1d1f21}
@media (prefers-color-scheme:light){:root{--text-color:#333;--bg-color:#EEE}}
.h-captcha{min-height:85px;display:block}
.red{color:red;font-weight:bold}
a,a:visited{color:var(--text-color)}
body,html{height:100%%}
body{display:flex;flex-direction:column;background-color:var(--bg-color);color:var(--text-color);font-family:Helvetica,Arial,sans-serif;max-width:1200px;margin:0 auto;padding: 0 20px}
details{transition: border-left-color 0.5s;max-width:1200px;text-align:left;border-left: 2px solid var(--text-color);padding:10px}
code{background-color:#dfdfdf30;border-radius:3px;padding:0 3px;}
img,h3,p{margin:0 0 5px 0}
footer{font-size:x-small;margin-top:auto;margin-bottom:20px;text-align:center}
img{display:inline}
.pt{padding-top:15vh;display:flex;align-items: center}
.pt img{margin-right:10px}
details[open]{border-left-color: #1400ff}
.lds-ring{display:inline-block;position:relative;width:80px;height:80px}.lds-ring div{box-sizing:border-box;display:block;position:absolute;width:32px;height:32px;margin:10px;border:5px solid var(--text-color);border-radius:50%%;animation:lds-ring 1.2s cubic-bezier(0.5, 0, 0.5, 1) infinite;border-color:var(--text-color) transparent transparent transparent}.lds-ring div:nth-child(1){animation-delay:-0.45s}.lds-ring div:nth-child(2){animation-delay:-0.3s}.lds-ring div:nth-child(3){animation-delay:-0.15s}@keyframes lds-ring{0%%{transform:rotate(0deg)}100%%{transform:rotate(360deg)}}
</style>
<noscript>
<style>.jsonly{display:none}</style>
</noscript>
</head>
<body data-pow="%s">
%s
%s
%s
<noscript>
<br>
<p class="red">JavaScript is required on this page.</p>
%s
</noscript>
<footer>
<img src="/img/footerlogo.png" />
<p>Security and Performance by <a href="https://BasedFlare.com">BasedFlare</a></p>
<p>Node: <code>%s</code></p>
</footer>
<script src="/js/sha1.js"></script>
</body>
</html>
]]
local noscript_extra_template = [[
<details>
<summary>No JavaScript?</summary>
<ol>
<li>
<p>Run this in a linux terminal:</p>
<code style="word-break: break-all;">
echo "Q0g9IiQxIjtCPSJiMDBiIjtJPTA7RElGRj0kKCgxNiMke0NIOjA6MX0gKiAyKSk7d2hpbGUgdHJ1ZTsgZG8gSD0kKGVjaG8gLW4gJENIJEkgfCBzaGExc3VtKTtFPSR7SDokRElGRjo0fTtbWyAkRSA9PSAkQiBdXSAmJiBlY2hvICRJICYmIGV4aXQgMDsoKEkrKykpO2RvbmU7Cg==" | base64 -d | bash -s %s
</code>
<li>Set a cookie named <code>z_ddos_pow</code> with the value as the number the script outputs, and path <code>/</code>.
<li>Remove <code>/bot-check?</code> from the url, and load the page again.
</ol>
</details>
]]
-- title with favicon and hostname
local site_name_section_template = [[
<h3 class="pt">
<img src="/favicon.ico" width="32" height="32">
%s
</h3>
]]
-- spinner animation for proof of work
local pow_section_template = [[
<h3>
Checking your browser for robots 🤖
</h3>
<div class="jsonly">
<div class="lds-ring"><div></div><div></div><div></div><div></div></div>
</div>
]]
-- message, hcaptcha form and submit button
local captcha_section_template = [[
<h3>
Please solve the captcha to continue.
</h3>
<form class="jsonly" method="POST">
<div class="h-captcha" data-sitekey="%s"></div>
<script src="https://hcaptcha.com/1/api.js" async defer></script>
<input type="submit" value="Calculating proof of work..." disabled>
</form>
]]
function _M.view(applet)
local response_body = ""
local response_status_code
if applet.method == "GET" then
-- get challenge string for proof of work
generated_work = utils.generate_secret(applet, pow_cookie_secret, true, "")
-- define body sections
local site_name_body = ""
local captcha_body = ""
local pow_body = ""
local noscript_extra_body = ""
-- check if captcha is enabled, path+domain priority, then just domain, and 0 otherwise
local captcha_enabled = false
local host = applet.headers['host'][0]
local path = applet.qs; --because on /bot-check?/whatever, .qs (query string) holds the "path"
local captcha_map_lookup = captcha_map:lookup(host..path) or captcha_map:lookup(host) or 0
captcha_map_lookup = tonumber(captcha_map_lookup)
if captcha_map_lookup == 2 then
captcha_enabled = true
end
--
-- pow at least is always enabled when reaching bot-check page
site_name_body = string.format(site_name_section_template, host)
if captcha_enabled then
captcha_body = string.format(captcha_section_template, captcha_sitekey)
else
pow_body = pow_section_template
noscript_extra_body = string.format(noscript_extra_template, generated_work)
end
-- sub in the body sections
response_body = string.format(body_template, generated_work, site_name_body, pow_body, captcha_body, noscript_extra_body, ray_id)
response_status_code = 403
elseif applet.method == "POST" then
local parsed_body = url.parseQuery(applet.receive(applet))
if parsed_body["h-captcha-response"] then
local hcaptcha_url = string.format(
"https://%s/siteverify",
core.backends["hcaptcha"].servers["hcaptcha"]:get_addr()
)
local hcaptcha_body = url.buildQuery({
secret=captcha_secret,
response=parsed_body["h-captcha-response"]
})
local httpclient = core.httpclient()
local res = httpclient:post{
url=hcaptcha_url,
body=hcaptcha_body,
headers={
[ "host" ] = { captcha_provider_domain },
[ "content-type" ] = { "application/x-www-form-urlencoded" }
}
}
local status, api_response = pcall(json.decode, res.body)
--require("print_r")
--print_r(hcaptcha_body)
--print_r(res)
--print_r(api_response)
if not status then
api_response = {}
end
if api_response.success == true then
local floating_hash = utils.generate_secret(applet, hcaptcha_cookie_secret, true, nil)
applet:add_header(
"set-cookie",
string.format("z_ddos_captcha=%s; expires=Thu, 31-Dec-37 23:55:55 GMT; Path=/; SameSite=Strict; Secure=true;", floating_hash)
)
end
end
-- if failed captcha, will just get sent back here so 302 is fine
response_status_code = 302
applet:add_header("location", applet.qs)
else
-- other methods
response_status_code = 403
end
applet:set_status(response_status_code)
applet:add_header("content-type", "text/html; charset=utf-8")
applet:add_header("content-length", string.len(response_body))
applet:start_response()
applet:send(response_body)
end
-- check if captcha is enabled, path+domain priority, then just domain, and 0 otherwise
function _M.decide_checks_necessary(txn)
local host = txn.sf:hdr("Host")
local path = txn.sf:path();
local captcha_map_lookup = captcha_map:lookup(host..path) or captcha_map:lookup(host) or 0
captcha_map_lookup = tonumber(captcha_map_lookup)
if captcha_map_lookup == 1 then
txn:set_var("txn.validate_pow", true)
elseif captcha_map_lookup == 2 then
txn:set_var("txn.validate_captcha", true)
txn:set_var("txn.validate_pow", true)
end
-- otherwise, domain+path was set to 0 (whitelist) or there is no entry in the map
end
-- check if captcha token is valid, separate secret from POW
function _M.check_captcha_status(txn)
local parsed_request_cookies = cookie.get_cookie_table(txn.sf:hdr("Cookie"))
local expected_cookie = utils.generate_secret(txn, hcaptcha_cookie_secret, false, nil)
if parsed_request_cookies["z_ddos_captcha"] == expected_cookie then
return txn:set_var("txn.captcha_passed", true)
end
end
-- check if pow token is valid
function _M.check_pow_status(txn)
local parsed_request_cookies = cookie.get_cookie_table(txn.sf:hdr("Cookie"))
if parsed_request_cookies["z_ddos_pow"] then
local generated_work = utils.generate_secret(txn, pow_cookie_secret, false, "")
local iterations = parsed_request_cookies["z_ddos_pow"]
local completed_work = sha.sha1(generated_work .. iterations)
local challenge_offset = tonumber(generated_work:sub(1,1),16) * 2
if completed_work:sub(challenge_offset+1, challenge_offset+4) == 'b00b' then -- i dont know lua properly :^)
return txn:set_var("txn.pow_passed", true)
end
end
end
return _M