smartcar-webhooks

Smartcar Webhooks

When to Use This Skill

• How do I receive Smartcar webhooks?
• How do I verify the Smartcar SC-Signature header?
• How do I respond to the Smartcar VERIFY challenge so my webhook activates?
• How do I handle VEHICLE_STATE and VEHICLE_ERROR events?
• Why is my Smartcar webhook signature verification failing?

Verification (core)

Smartcar signs every webhook with a hex-encoded HMAC-SHA256 of the raw request body, keyed with your Application Management Token (AMT, from the Smartcar Dashboard), in the SC-Signature header. On setup Smartcar also POSTs a one-time VERIFY event whose data.challenge you must hash with the same AMT and echo back within 15 seconds — otherwise the webhook never activates. This is Smartcar's own scheme, not the Standard Webhooks spec.

The official SDKs expose two helpers: hashChallenge/hash_challenge (hex HMAC of any string) and verifyPayload/verify_payload (compares the header against the body's HMAC).

Node (Express, Next.js):

const smartcar = require('smartcar');
const AMT = process.env.SMARTCAR_MANAGEMENT_TOKEN;

// 1. VERIFY handshake — echo the hashed challenge so the webhook activates
if (event.eventType === 'VERIFY') {
  const hmac = smartcar.hashChallenge(AMT, event.data.challenge); // hex string
  return res.status(200).json({ challenge: hmac });
}

// 2. Data events — verify SC-Signature (hex HMAC-SHA256 of the raw body).
//    The Node SDK re-serializes the parsed body internally, so pass the object.
if (!smartcar.verifyPayload(AMT, req.headers['sc-signature'], event)) {
  return res.status(401).send('Invalid signature');
}

Python (FastAPI) — the SDK hashes the raw body string you pass in:

import smartcar
amt = os.environ["SMARTCAR_MANAGEMENT_TOKEN"]

if event["eventType"] == "VERIFY":
    return {"challenge": smartcar.hash_challenge(amt, event["data"]["challenge"])}

if not smartcar.verify_payload(amt, request.headers["sc-signature"], raw_body):
    raise HTTPException(status_code=401, detail="Invalid signature")