A serverless webhook endpoint needs to validate that it is a legitimate Event Grid subscriber before receiving events. Which Event Grid validation mechanism must it handle?

1. A OAuth token verification
2. ✓ B Subscription validation handshake (return validationCode) (correct answer)
3. C Mutual TLS
4. D IP whitelisting

Shortcut: When creating a webhook subscription, Event Grid sends a SubscriptionValidationEvent containing a validationCode. The handler must return the code in the response within 5 minutes to confirm ownership.