Your checkout. Relay's fulfillment. One clean handoff.

import crypto from "node:crypto";

// Relay now sends a timestamped v2 signature and keeps the
// legacy signature header during migration.
export function verifyRelay(
  rawBody: string,
  timestamp: string,
  signatureV2: string,
  secret: string,
) {
  const expected = crypto
    .createHmac("sha256", secret)
    .update(`${timestamp}.${rawBody}`)
    .digest("hex");

  const ageSeconds = Math.abs(Math.floor(Date.now() / 1000) - Number(timestamp));
  if (!Number.isFinite(Number(timestamp)) || ageSeconds > 300) {
    return false;
  }

  return crypto.timingSafeEqual(
    Buffer.from(expected, "hex"),
    Buffer.from(signatureV2, "hex"),
  );
}

// In your handler:
app.post("/webhooks/relay", (req, res) => {
  const sig = req.header("x-relay-signature-v2");
  const timestamp = req.header("x-relay-timestamp");
  const raw = req.rawBody;                         // raw buffer, not parsed JSON
  if (!sig || !timestamp || !verifyRelay(raw, timestamp, sig, process.env.RELAY_WEBHOOK_SECRET!)) {
    return res.status(401).end();
  }

  const { event, data } = JSON.parse(raw);
  // event === "order.status_changed"
  // data.status in: accepted | assigned | picked_up | in_transit | delivered | failed | cancelled
  handleRelayEvent(event, data);
  res.status(200).end();
});