Microsoft SharePoint Webhooks Skill

When to Use This Skill

• Setting up Microsoft SharePoint list or document-library webhook handlers
• Completing the SharePoint validationtoken subscription handshake
• Validating the clientState shared secret on incoming notifications
• Understanding the thin SharePoint notification payload
• Reacting to list-item changes (ItemAdded, ItemUpdated, ItemDeleted) via the GetChanges API

How SharePoint Webhooks Differ

SharePoint webhooks are not HMAC-signed and are not Standard Webhooks. There is no request signature. Authenticity relies on two things instead:

1. Validation handshake — when a subscription is created (or its notificationUrl changes), SharePoint POSTs with a validationtoken query-string parameter. Your endpoint must echo that exact token back as an HTTP 200 text/plain body within ~5 seconds, or the subscription is never created.
2. clientState — an opaque string you set at subscription time. SharePoint echoes it in the clientState field of every notification. Compare it to your stored secret as a shared-secret sanity check. It is the only per-message identity signal (not a signature).

Notifications are thin and batched under a value array and carry no change details — you call the list GetChanges API with a stored change token to learn what actually changed.

Verification (core)

const crypto = require('crypto');

// 1. Validation handshake — runs BEFORE any body parsing.
//    Echo the validationtoken query param back verbatim as text/plain.
const token = new URL(req.url, 'http://localhost').searchParams.get('validationtoken');
if (token) {
  res.setHeader('Content-Type', 'text/plain');
  return res.status(200).send(token);   // must reply within ~5s or creation fails
}

// 2. clientState — timing-safe compare the shared secret on every notification.
function clientStateMatches(received, expected) {
  if (typeof received !== 'string' || typeof expected !== 'string') return false;
  const a = Buffer.from(received);
  const b = Buffer.from(expected);
  if (a.length !== b.length) return false;
  return crypto.timingSafeEqual(a, b);
}

const { value = [] } = JSON.parse(rawBody);   // thin, batched notifications
const ok = value.every(n => clientStateMatches(n.clientState, process.env.SHAREPOINT_CLIENT_STATE));
if (!ok) return res.status(400).send('Invalid clientState');
// Notifications carry no change details — call list GetChanges with your stored change token.

For complete handlers with route wiring, GetChanges follow-up, and tests, see:

• examples/express/
• examples/nextjs/
• examples/fastapi/

Notification Payload

Each notification in the batch has this shape (no change details):

{
  "value": [
    {
      "subscriptionId": "91779246-afe9-4525-b122-6c199ae89211",
      "clientState": "your-opaque-secret",
      "expirationDateTime": "2016-04-30T17:27:00.0000000Z",
      "resource": "b9f6f714-9df8-470b-b22e-653855e1c181",
      "tenantId": "00000000-0000-0000-0000-000000000000",
      "siteUrl": "/",
      "webId": "dbc5a806-e4d4-46e5-951c-6344d70b62fa"
    }
  ]
}

resource is the list GUID. To learn what changed, call GetChanges on that list.

Change Types (from GetChanges)

The notification does not carry the event type. After a notification you call GetChanges and inspect each change's ChangeType:

For the full change reference, see SharePoint list webhooks.

Environment Variables

SHAREPOINT_CLIENT_STATE=your-opaque-secret   # clientState set at subscription time

Local Development

# Start tunnel (no account needed)
npx hookdeck-cli listen 3000 microsoft-sharepoint --path /webhooks/microsoft-sharepoint

Reference Materials

• references/overview.md - SharePoint webhook concepts, change types
• references/setup.md - Creating and renewing subscriptions
• references/verification.md - Handshake and clientState details