DROP Webhook Notifications
Optional outbound HTTPS webhook notifications from DROP to a data broker's endpoint, enabled in the Data Broker Portal notification settings. Five event types (download.ready, upload.received, upload.processed, amendment.received, amendment.processed) are delivered with X-Webhook-* headers and an HMAC-SHA256 signature over "." using a per-broker signing secret. Documented in prose in the DROP technical reference and the OpenAPI info block; no AsyncAPI is published.