# 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.

```javascript
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
  }
}

```

> For complete handlers with route wiring, event dispatch, and tests, see:
> 
> * [examples/express/](https://github.com/hookdeck/webhook-skills/tree/main/skills/courier-webhooks/examples/express/)
> * [examples/nextjs/](https://github.com/hookdeck/webhook-skills/tree/main/skills/courier-webhooks/examples/nextjs/)
> * [examples/fastapi/](https://github.com/hookdeck/webhook-skills/tree/main/skills/courier-webhooks/examples/fastapi/)

## Event Payload Structure

Every webhook uses a consistent envelope:

```json
{
  "type": "message:updated",
  "data": { "...": "event-specific fields" }
}

```

Dispatch on the top-level `type`, then read event details from `data`.

## Common Event Types

| Event | Triggered When |
| --- | --- |
| `message:updated` | A message's delivery status changes (carries status + timestamps in `data`) |
| `notification:submitted` | A notification is submitted for sending |
| `notification:submission_canceled` | A submitted notification is canceled |
| `notification:published` | A notification template is published |
| `audiences:updated` | An audience definition is updated |
| `audiences:user:matched` | A user starts matching an audience |
| `audiences:user:unmatched` | A user stops matching an audience |
| `audiences:calculated` | An audience membership recalculation completes |

> Note: Courier does not emit per-status events (there is no `message:delivered`,
> `message:opened`, or `message:clicked`). A single `message:updated` event carries the
> current status and timestamps inside `data`.

> For the full event reference, see [Courier Outbound Webhooks](https://www.courier.com/docs/platform/workspaces/outbound-webhooks).

## Environment Variables

```bash
COURIER_WEBHOOK_SECRET=your_webhook_signing_secret   # From the webhook settings in Courier

```

## Local Development

```bash
# Start tunnel (no account needed)
npx hookdeck-cli listen 3000 courier --path /webhooks/courier

```

## Reference Materials

* [references/overview.md](https://github.com/hookdeck/webhook-skills/blob/main/skills/courier-webhooks/references/overview.md) - Courier webhook concepts and events
* [references/setup.md](https://github.com/hookdeck/webhook-skills/blob/main/skills/courier-webhooks/references/setup.md) - Dashboard configuration and signing secret
* [references/verification.md](https://github.com/hookdeck/webhook-skills/blob/main/skills/courier-webhooks/references/verification.md) - Signature verification details and gotchas