Move POW proof checking to POST and sign a cookie there, kinda like captcha flow, so we can do a more intensive one without it happening on every request. We just check the hmac now.

Still TODO actually converting it to argon, but should be straightforward from this point.
Another advantage of making POW check use POST is a better noscript experience. We now provide a box and "submit" button, so they don't have to mess with setting a cookie.

haproxy/js/challenge.js

@@ -2,18 +2,30 @@ function finishRedirect() {
 	window.location=location.search.slice(1)+location.hash || "/";
 }
 
-function finishPow(combined, answer) {
-	document.cookie='z_ddos_pow='+combined+'#'+answer+';expires=Thu, 31-Dec-37 23:55:55 GMT; path=/; SameSite=Strict; '+(location.protocol==='https:'?'Secure=true; ':'');
-	const hasCaptchaForm = document.querySelector('form');
-	if (!hasCaptchaForm) {
-		finishRedirect();
+function postResponse(powResponse, captchaResponse) {
+	const body = {
+		'pow_response': powResponse,
+	};
+	if (captchaResponse) {
+		body['h-captcha-response'] = captchaResponse;
+		body['g-recaptcha-response'] = captchaResponse;
 	}
+	fetch('/bot-check', {
+		method: 'POST',
+		headers: {
+		  'Content-Type': 'application/x-www-form-urlencoded',
+		},
+		body: new URLSearchParams(body),
+		redirect: 'manual',
+	}).then(res => {
+		finishRedirect();
+	})
 }
 
 const powFinished = new Promise((resolve, reject) => {
 	window.addEventListener('DOMContentLoaded', (event) => {
 		const combined = document.querySelector('[data-pow]').dataset.pow;
-		const [_userkey, challenge, _signature] = combined.split("#");
+		const [userkey, challenge, signature] = combined.split("#");
 		const start = Date.now();
 		if (window.Worker && crypto.subtle) {
 			const threads = Math.min(2,Math.ceil(window.navigator.hardwareConcurrency/2));
@@ -26,8 +38,7 @@ const powFinished = new Promise((resolve, reject) => {
 				console.log('Worker', workerId, 'returned answer', answer, 'in', Date.now()-start+'ms');
 				const dummyTime = 5000 - (Date.now()-start);
 				window.setTimeout(() => {
-					finishPow(combined, answer);
-					resolve();
+					resolve(`${combined}#${answer}`);
 				}, dummyTime);
 			}
 			const workers = [];
@@ -53,31 +64,24 @@ const powFinished = new Promise((resolve, reject) => {
 			}
 			const dummyTime = 5000 - (Date.now()-start);
 			window.setTimeout(() => {
-				finishPow(combined, i);
-				resolve();
+				resolve(`${combined}#${i}`);
 			}, dummyTime);
 		}
 	});
+}).then((powResponse) => {
+	const hasCaptchaForm = document.getElementById('captcha');
+	if (!hasCaptchaForm) {
+		postResponse(powResponse);
+	}
+	return powResponse;
 });
 
-function onCaptchaSubmit(callback) {
+function onCaptchaSubmit(captchaResponse) {
 	const captchaElem = document.querySelector('[data-sitekey]');
 	captchaElem.insertAdjacentHTML('afterend', `<div class="lds-ring"><div></div><div></div><div></div><div></div></div>`);
 	captchaElem.remove();
-	powFinished.then(() => {
-		fetch('/bot-check', {
-			method: 'POST',
-			headers: {
-			  'Content-Type': 'application/x-www-form-urlencoded',
-			},
-			body: new URLSearchParams({
-				'h-captcha-response': callback,
-				'g-recaptcha-response': callback,
-			}),
-			redirect: 'manual',
-		}).then(res => {
-			finishRedirect();
-		})
+	powFinished.then((powResponse) => {
+		postResponse(powResponse, captchaResponse);
 	});
 }
 

src/scripts/hcaptcha.lua

@@ -116,8 +116,11 @@ local noscript_extra_template = [[
 						<code style="word-break: break-all;">
 							echo "Q0g9IiQyIjtCPSIwMDQxIjtJPTA7RElGRj0kKCgxNiMke0NIOjA6MX0gKiAyKSk7d2hpbGUgdHJ1ZTsgZG8gSD0kKGVjaG8gLW4gJENIJEkgfCBzaGEyNTZzdW0pO0U9JHtIOiRESUZGOjR9O1tbICRFID09ICRCIF1dICYmIGVjaG8gJDEjJDIjJDMjJEkgJiYgZXhpdCAwOygoSSsrKSk7ZG9uZTs=" | base64 -d | bash -s %s %s %s
 						</code>
-					<li>Set a cookie named <code>z_ddos_pow</code> with the value as the script output, and path <code>/</code>.
-					<li>Remove <code>/bot-check?</code> from the url, and reload the page.
+					<li>Paste the output from the script into the box and submit:
+					<form method="POST">
+						<textarea type="text" name="pow_response"></textarea>
+						<input type="submit" value="submit" />
+					</form>
 				</ol>
 			</details>
 ]]
@@ -145,25 +148,26 @@ local captcha_section_template = [[
 		<h3>
 			Please solve the captcha to continue.
 		</h3>
-		<form class="jsonly" method="POST">
+		<div id="captcha" class="jsonly">
 			<div class="%s" data-sitekey="%s" data-callback="onCaptchaSubmit"></div>
 			<script src="%s" async defer></script>
-		</form>
+		</div>
 ]]
 
 function _M.view(applet)
+
+	-- set response body and declare status code
 	local response_body = ""
 	local response_status_code
+
+	-- if request is GET, serve the challenge page
 	if applet.method == "GET" then
+
 		-- get the user_key#challenge#sig
 		local user_key = sha.bin_to_hex(randbytes(16))
 		local challenge_hash = utils.generate_secret(applet, pow_cookie_secret, user_key, true)
 		local signature = sha.hmac(sha.sha256, hmac_cookie_secret, user_key .. challenge_hash)
 		local combined_challenge = user_key .. "#" .. challenge_hash .. "#" .. signature
-		-- print_r(user_key)
-		-- print_r(challenge_hash)
-		-- print_r(signature)
-		-- print_r(combined_challenge)
 
 		-- define body sections
 		local site_name_body = ""
@@ -194,19 +198,34 @@ function _M.view(applet)
 		-- sub in the body sections
 		response_body = string.format(body_template, combined_challenge, site_name_body, pow_body, captcha_body, noscript_extra_body, ray_id)
 		response_status_code = 403
+
+	-- if request is POST, check the answer to the pow/cookie
 	elseif applet.method == "POST" then
+
+		-- parsed POST body
 		local parsed_body = url.parseQuery(applet.receive(applet))
+
+		-- whether to set cookies sent as secure or not
+		local secure_cookie_flag = " Secure=true;"
+		if applet.sf:ssl_fc() == "0" then
+			secure_cookie_flag = ""
+		end
+
+		-- handle setting the captcha cookie
 		local user_captcha_response = parsed_body["h-captcha-response"] or parsed_body["g-recaptcha-response"]
 		if user_captcha_response then
+			-- format the url for verifying the captcha response
 			local captcha_url = string.format(
 				"https://%s%s",
 				core.backends[captcha_backend_name].servers[captcha_backend_name]:get_addr(),
 				captcha_siteverify_path
 			)
+			-- construct the captcha body to send to the captcha url
 			local captcha_body = url.buildQuery({
 				secret=captcha_secret,
 				response=user_captcha_response
 			})
+			-- instantiate an http client and make the request
 			local httpclient = core.httpclient()
 			local res = httpclient:post{
 				url=captcha_url,
@@ -216,42 +235,90 @@ function _M.view(applet)
 					[ "content-type" ] = { "application/x-www-form-urlencoded" }
 				}
 			}
+			-- try parsing the response as json
 			local status, api_response = pcall(json.decode, res.body)
 			if not status then
 				api_response = {}
 			end
+			-- the response was good i.e the captcha provider says they passed, give them a cookie
 			if api_response.success == true then
-				-- for captcha, they dont need to solve a POW but we check the user_hash and sig later
+
 				local user_key = sha.bin_to_hex(randbytes(16))
 				local user_hash = utils.generate_secret(applet, captcha_cookie_secret, user_key, true)
 				local signature = sha.hmac(sha.sha256, hmac_cookie_secret, user_key .. user_hash)
 				local combined_cookie = user_key .. "#" .. user_hash .. "#" .. signature
-				local secure_cookie_flag = " Secure=true;"
-				if applet.sf:ssl_fc() == "0" then
-					secure_cookie_flag = ""
-				end
 				applet:add_header(
 					"set-cookie",
 					string.format(
-						"z_ddos_captcha=%s; Expires=Thu, 31-Dec-37 23:55:55 GMT; Path=/; SameSite=Strict;",
+						"z_ddos_captcha=%s; Expires=Thu, 31-Dec-37 23:55:55 GMT; Path=/; SameSite=Strict;%s",
 						combined_cookie,
 						secure_cookie_flag
 					)
 				)
+
 			end
 		end
-		-- if failed captcha, will just get sent back here so 302 is fine
+
+		-- handle setting the POW cookie
+		local user_pow_response = parsed_body["pow_response"]
+		if user_pow_response then
+			-- split the response up (makes the nojs submission easier because it can be a single field)
+			local split_response = utils.split(user_pow_response, "#")
+			if #split_response == 4 then
+				local given_user_key = split_response[1]
+				local given_challenge_hash = split_response[2]
+				local given_signature = split_response[3]
+				local given_answer = split_response[4]
+				-- regenerate the challenge and compare it
+				local generated_challenge_hash = utils.generate_secret(applet, pow_cookie_secret, given_user_key, true)
+				if given_challenge_hash == generated_challenge_hash then
+
+					-- regenerate the signature and compare it
+					local generated_signature = sha.hmac(sha.sha256, hmac_cookie_secret, given_user_key .. given_challenge_hash)
+					if given_signature == generated_signature then
+
+						-- do the work with their given answer
+						local completed_work = sha.sha256(generated_challenge_hash .. given_answer) -- (TODO: replace this bit with argon2)
+
+						-- check the output is correct
+						local challenge_offset = tonumber(generated_challenge_hash:sub(1,1),16) * 2
+						if completed_work:sub(challenge_offset+1, challenge_offset+4) == '0041' then
+
+							-- the answer was good, give them a cookie
+							local signature = sha.hmac(sha.sha256, hmac_cookie_secret, given_user_key .. given_challenge_hash .. given_answer)
+							local combined_cookie = given_user_key .. "#" .. given_challenge_hash .. "#" .. given_answer .. "#" .. signature
+							applet:add_header(
+								"set-cookie",
+								string.format(
+									"z_ddos_pow=%s; Expires=Thu, 31-Dec-37 23:55:55 GMT; Path=/; SameSite=Strict;%s",
+									combined_cookie,
+									secure_cookie_flag
+								)
+							)
+
+						end
+					end
+				end
+			end
+		end
+
+		-- redirect them to their desired page in applet.qs (query string)
+		-- if they didn't get the appropriate cookies they will be sent back to the challenge page
 		response_status_code = 302
 		applet:add_header("location", applet.qs)
+
+	-- else if its another http method, just 403 them
 	else
-		-- other methods
 		response_status_code = 403
 	end
+
+	-- finish sending the response
 	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
@@ -273,6 +340,7 @@ end
 function _M.check_captcha_status(txn)
 	local parsed_request_cookies = cookie.get_cookie_table(txn.sf:hdr("Cookie"))
 	local received_captcha_cookie = parsed_request_cookies["z_ddos_captcha"] or ""
+	-- split the cookie up
 	local split_cookie = utils.split(received_captcha_cookie, "#")
 	if #split_cookie ~= 3 then
 		return
@@ -303,22 +371,16 @@ function _M.check_pow_status(txn)
 	end
 	local given_user_key = split_cookie[1]
 	local given_challenge_hash = split_cookie[2]
-	local given_signature = split_cookie[3]
-	local given_nonce = split_cookie[4]
+	local given_answer = split_cookie[3]
+	local given_signature = split_cookie[4]
 	-- regenerate the challenge and compare it
 	local generated_challenge_hash = utils.generate_secret(txn, pow_cookie_secret, given_user_key, false)
 	if given_challenge_hash ~= generated_challenge_hash then
 		return
 	end
 	-- regenerate the signature and compare it
-	local generated_signature = sha.hmac(sha.sha256, hmac_cookie_secret, given_user_key .. given_challenge_hash)
-	if given_signature ~= generated_signature then
-		return
-	end
-	-- check the work
-	local completed_work = sha.sha256(generated_challenge_hash .. given_nonce)
-	local challenge_offset = tonumber(generated_challenge_hash:sub(1,1),16) * 2
-	if completed_work:sub(challenge_offset+1, challenge_offset+4) == '0041' then -- i dont know lua properly :^)
+	local generated_signature = sha.hmac(sha.sha256, hmac_cookie_secret, given_user_key .. given_challenge_hash .. given_answer)
+	if given_signature == generated_signature then
 		return txn:set_var("txn.pow_passed", true)
 	end
 end