Webhooks

import { createHmac, timingSafeEqual } from 'node:crypto';

const MAX_AGE_SECONDS = 5 * 60; // reject deliveries older than 5 minutes

// rawBody: the exact bytes you received (a Buffer or string), before JSON.parse.
// headers: the request headers, with lowercase names.
export function verifyCommentGate(rawBody, headers, secret) {
  const timestamp = String(headers['x-commentgate-timestamp'] ?? '');
  const signature = String(headers['x-commentgate-signature-v2'] ?? '');
  if (!/^\d+$/.test(timestamp)) return false;
  if (Math.abs(Date.now() / 1000 - Number(timestamp)) > MAX_AGE_SECONDS) return false;

  // The signature covers "<timestamp>.<raw body>", so an old delivery
  // cannot be replayed with a new timestamp.
  const expected =
    'v2=' + createHmac('sha256', secret).update(timestamp + '.').update(rawBody).digest('hex');
  return (
    signature.length === expected.length &&
    timingSafeEqual(Buffer.from(signature), Buffer.from(expected))
  );
}

import express from 'express';
import { verifyCommentGate } from './verify.js';

const app = express();
const seen = new Set(); // use your database in production

// express.raw keeps the body as bytes, so the signature can be checked
app.post('/commentgate', express.raw({ type: 'application/json' }), (req, res) => {
  if (!verifyCommentGate(req.body, req.headers, process.env.COMMENTGATE_SIGNING_SECRET)) {
    return res.sendStatus(401);
  }
  const delivery = JSON.parse(req.body.toString('utf8'));
  if (seen.has(delivery.id)) return res.sendStatus(200); // a retry: already handled
  seen.add(delivery.id);

  // Answer fast, then do the work
  res.sendStatus(200);
  console.log(delivery.event, delivery.comment?.text);
});

app.listen(3000);

import hashlib, hmac, time

MAX_AGE_SECONDS = 5 * 60  # reject deliveries older than 5 minutes

def verify_commentgate(raw_body: bytes, headers, secret: str) -> bool:
    timestamp = headers.get("x-commentgate-timestamp", "")
    signature = headers.get("x-commentgate-signature-v2", "")
    if not timestamp.isdigit() or abs(time.time() - int(timestamp)) > MAX_AGE_SECONDS:
        return False
    # The signature covers "<timestamp>.<raw body>", so an old delivery
    # cannot be replayed with a new timestamp.
    signed = timestamp.encode() + b"." + raw_body
    expected = "v2=" + hmac.new(secret.encode(), signed, hashlib.sha256).hexdigest()
    return hmac.compare_digest(signature, expected)