Microsoft SharePoint Webhooks

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.