courier-webhooks

Courier Webhooks

When to Use This Skill

• How do I receive Courier outbound webhooks?
• How do I verify the Courier courier-signature header?
• How do I handle message:updated status changes or notification:submitted events?
• Why is my Courier webhook signature verification failing?

Verification (core)

Courier signs every outbound webhook with HMAC-SHA256. The courier-signature header carries a timestamp and hex signature: t=<timestamp>,signature=<hex_digest>. The signed content is `${timestamp}.${rawBody}` — the timestamp, a literal dot, then the raw request body (do not JSON.parse before verifying). Courier has no webhook-verification SDK, so verify manually and compare in constant time.

Courier does not document whether t is in seconds or milliseconds, so normalize it before the staleness comparison instead of assuming a unit. The 5-minute tolerance below is this skill's default, not a window Courier publishes — tune it to your needs.

const crypto = require('crypto');

// The unit of `t` is not documented. A ~10-digit value is seconds, a ~13-digit
// value is milliseconds — normalize to ms either way.
function toMillis(timestamp) {
  const value = Number(timestamp);
  if (!Number.isFinite(value)) return NaN;
  return Math.abs(value) < 1e11 ? value * 1000 : value;
}

function verifyCourierWebhook(rawBody, signatureHeader, secret, toleranceMs = 5 * 60 * 1000) {
  if (!signatureHeader) return false;
  const parts = {};
  for (const segment of signatureHeader.split(',')) {
    const i = segment.indexOf('=');
    if (i !== -1) parts[segment.slice(0, i).trim()] = segment.slice(i + 1).trim();
  }
  const { t: timestamp, signature } = parts;
  if (!timestamp || !signature) return false;

  // Reject stale deliveries (accepts a seconds or milliseconds timestamp)
  const ts = toMillis(timestamp);
  if (!Number.isFinite(ts) || Math.abs(Date.now() - ts) > toleranceMs) return false;

  const expected = crypto
    .createHmac('sha256', secret)
    .update(`${timestamp}.${rawBody}`)      // timestamp + "." + raw body
    .digest('hex');                          // raw body, not JSON.stringify — see references/verification.md
  try {
    return crypto.timingSafeEqual(Buffer.from(signature, 'hex'), Buffer.from(expected, 'hex'));
  } catch {
    return false; // length mismatch = invalid
  }
}