# eBay Webhooks

## When to Use This Skill

* How do I receive eBay webhooks (notifications)?
* How do I pass eBay's endpoint challenge validation (`challenge_code`)?
* How do I verify the `x-ebay-signature` header (ECDSA)?
* How do I use the eBay `getPublicKey` endpoint and cache the public key?
* How do I handle `MARKETPLACE_ACCOUNT_DELETION` (marketplace account deletion / closure) notifications?
* Why is my eBay signature verification failing?

## How eBay Webhooks Differ From Most Providers

eBay does not use HMAC with a shared secret, and does not follow the
Standard Webhooks spec. Two distinct mechanisms are involved:

1. Endpoint challenge (one-time, on save) — When you register or update a
  destination, eBay sends `GET https://<your-endpoint>?challenge_code=...`.
  You must respond HTTP 200 with JSON `{"challengeResponse":"<hex>"}` where
  the hex is the SHA-256 hash of exactly `challengeCode + verificationToken
  
  * endpoint` — in that order. The order is mandatory.
2. Per-notification signature (ECDSA) — Every notification carries an
  `x-ebay-signature` header: a Base64-encoded JSON object with fields
  `alg`, `kid`, `signature`, and `digest`. Use the `kid` to fetch the matching
  public key via `getPublicKey`, then verify the ECDSA signature over the
  raw request body. Cache the public key ~1 hour (keyed by `kid`).

## Verification (core)

Endpoint challenge — deterministic SHA-256, no crypto keys needed:

```javascript
const crypto = require('crypto');

function challengeResponse(challengeCode, verificationToken, endpoint) {
  // ORDER IS MANDATORY: challengeCode + verificationToken + endpoint
  const hash = crypto.createHash('sha256');
  hash.update(challengeCode);
  hash.update(verificationToken);
  hash.update(endpoint);
  return hash.digest('hex'); // return as { challengeResponse: <hex> } with HTTP 200
}

```

Per-notification signature — ECDSA over the raw body, key fetched by `kid`:

```javascript
async function verifyEbaySignature(rawBody, signatureHeader, getPublicKey) {
  if (!signatureHeader) return false;
  let sig;
  try { sig = JSON.parse(Buffer.from(signatureHeader, 'base64').toString('utf8')); }
  catch { return false; }              // { alg, kid, signature, digest }
  if (!sig.kid || !sig.signature) return false;
  const pem = await getPublicKey(sig.kid); // cache ~1h, keyed by kid
  const verifier = crypto.createVerify('sha1'); // eBay signs ECDSA with SHA-1
  verifier.update(rawBody);            // RAW body bytes — do not re-serialize
  verifier.end();
  try { return verifier.verify(pem, sig.signature, 'base64'); }
  catch { return false; }
}

```

> For complete handlers with the challenge route, the `getPublicKey` fetch +
> LRU cache, event dispatch, and tests, see:
> 
> * [examples/express/](https://github.com/hookdeck/webhook-skills/tree/main/skills/ebay-webhooks/examples/express/)
> * [examples/nextjs/](https://github.com/hookdeck/webhook-skills/tree/main/skills/ebay-webhooks/examples/nextjs/)
> * [examples/fastapi/](https://github.com/hookdeck/webhook-skills/tree/main/skills/ebay-webhooks/examples/fastapi/)

> Official SDK (Node.js): eBay publishes
> [`event-notification-nodejs-sdk`](https://github.com/eBay/event-notification-nodejs-sdk),
> which wraps the exact algorithm above (`EventNotificationSDK.process(...)` for
> signatures, `validateEndpoint(...)` for the challenge). The examples use a
> transparent manual implementation so they are testable offline without the
> OAuth call that `getPublicKey` requires — see
> [references/verification.md](https://github.com/hookdeck/webhook-skills/blob/main/skills/ebay-webhooks/references/verification.md) for the SDK path.

## Common Event Types (Topics)

| Topic | Triggered When |
| --- | --- |
| `MARKETPLACE_ACCOUNT_DELETION` | An eBay user closed their account / requested personal-data deletion. All developers must subscribe or opt out. |
| `AUTHORIZATION_REVOCATION` | A user revoked your app's authorization — stop making API calls on their behalf and clean up stored tokens. |
| `ITEM_AVAILABILITY` | Availability of a subscribed item changed |
| `ITEM_PRICE_REVISION` | Price of a subscribed item was revised |
| `PRIORITY_LISTING_REVISION` | A priority listing was revised |

The topic arrives in the payload at `metadata.topic`. The full, current list of
topics (and the OAuth scopes needed to subscribe) is returned by the
[`getTopics`](https://developer.ebay.com/api-docs/commerce/notification/resources/topic/methods/getTopics)
method — do not hard-code a list you cannot see.

## Environment Variables

```bash
EBAY_VERIFICATION_TOKEN=your_verification_token   # 32-80 chars, [A-Za-z0-9_-] only
EBAY_ENDPOINT=https://your-domain.com/webhooks/ebay  # EXACT public URL eBay calls
EBAY_CLIENT_ID=your_app_id                        # App credentials (getPublicKey OAuth)
EBAY_CLIENT_SECRET=your_cert_id
EBAY_ENV=production                               # sandbox | production

```

## Local Development

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

```

Use the forwarding URL as `EBAY_ENDPOINT` and as the destination URL you
register with eBay. The endpoint URL used in the SHA-256 challenge hash must
be the exact URL eBay calls (the public tunnel URL, not `localhost`).

## Reference Materials

* [references/overview.md](https://github.com/hookdeck/webhook-skills/blob/main/skills/ebay-webhooks/references/overview.md) - eBay notification concepts, topics, payloads
* [references/setup.md](https://github.com/hookdeck/webhook-skills/blob/main/skills/ebay-webhooks/references/setup.md) - Configure destinations, verification token, subscriptions
* [references/verification.md](https://github.com/hookdeck/webhook-skills/blob/main/skills/ebay-webhooks/references/verification.md) - Challenge + ECDSA signature details, SDK path, gotchas