Verify the Masnet signature in Node.js

Requirements in Masnet

Before configuring the receiving system, prepare the destination in Masnet. The steps are the same for every system.

1. Open Company › Integrations (the Spanish interface labels it Empresa › Integraciones), go to the Destinations tab and select New destination. If the integration has no authorized data yet, Masnet asks you to authorize it first.
2. In Destination address (https) enter the receiver public URL. It must be https, port 443 or 8443 and a public DNS name: user information in the URL, fragments, IP addresses and internal names are not accepted. A query string is allowed; Masnet treats the whole URL as a credential.
3. In Format choose Standard JSON (application/json) or Structured CloudEvents (application/cloudevents+json). The event content is the same; see Webhooks.
4. Select Create destination. Masnet shows the signing secret (whsec_…) only once. Store it immediately in the receiver secret store; it cannot be read again.
5. Select Test destination and then Send test. The integration is activated only after a successful test; then use Activate destination.

Data the verifier needs

• The destination signing secret (whsec_…), stored outside the code.
• The exact body received, uninterpreted. In Express use express.raw({ type: '*/*' }) on the webhook route, so that req.body is a Buffer; do not use express.json() before verifying.
• The webhook-id, webhook-timestamp and webhook-signature headers.
• A clock tolerance of 5 minutes, which is what the Standard Webhooks libraries apply and what is recommended for the receiver.

The signature is v1, followed by base64(HMAC-SHA256) computed with the binary key obtained by base64-decoding what follows whsec_, over the bytes webhook-id + . + webhook-timestamp + . + the exact body. Always verify over the received bytes, before parsing the JSON.

With the standardwebhooks library

Install standardwebhooks from npm. The library validates the 5-minute tolerance and multiple signatures.

// npm install standardwebhooks
import { Webhook } from 'standardwebhooks'

/**
 * `rawBody` is the unparsed request body (string or Buffer); `headers` holds webhook-id,
 * webhook-timestamp and webhook-signature. The library enforces a 5 minute tolerance.
 */
export function verify({ secret, headers, rawBody }) {
  try {
    new Webhook(secret).verify(rawBody, headers)
    return true
  } catch {
    return false
  }
}

Without dependencies

The function compares in constant time and accepts any of the signatures in the header.

import { createHmac, timingSafeEqual } from 'node:crypto'

/**
 * Verifies a Masnet webhook with node:crypto only.
 * `rawBody` must be the exact bytes received (Buffer or string), before any JSON parsing.
 */
export function verify({ secret, headers, rawBody, now = Date.now() / 1000, tolerance = 300 }) {
  const id = headers['webhook-id']
  const timestamp = headers['webhook-timestamp']
  const signatures = headers['webhook-signature']
  if (!id || !signatures || !/^\d+$/.test(timestamp ?? '')) return false
  if (Math.abs(now - Number(timestamp)) > tolerance) return false

  const key = Buffer.from(secret.replace(/^whsec_/, ''), 'base64')
  const expected = createHmac('sha256', key).update(`${id}.${timestamp}.`).update(rawBody).digest()

  // During a rotation the header carries two signatures separated by a space; any match is valid.
  return signatures.split(' ').some((part) => {
    const [version, value] = part.split(',')
    if (version !== 'v1' || !value) return false
    const given = Buffer.from(value, 'base64')
    return given.length === expected.length && timingSafeEqual(given, expected)
  })
}

Operation: duplicates and ordering

• Idempotency. webhook-id identifies the event and is kept across retries and redeliveries. Record the identifiers already processed and discard repeats with a 2xx response.
• Ordering. Each resource (subject) carries an increasing sequence. Discard an event whose sequence is lower than or equal to the last one applied for that subject. Events of different resources have no order between them.
• Retries. Masnet retries any non-2xx response for up to 72 hours; the full schedule is in Webhooks.
• Secret rotation. When rotating with overlap, the previous secret stays valid for 24 hours and webhook-signature carries two v1,… signatures separated by a space. Accept the event if either one matches.

Troubleshooting

Masnet records the response code of each attempt in the delivery history. These are the effects of each receiver response: