File uploads introduce risks beyond ordinary JSON APIs. Validate file size, content type, file signatures where appropriate, filename handling, storage location, and access permissions.

Never trust a client-provided filename or MIME type as proof of content. Generate server-side object names and store files outside executable application directories.

For large files, direct-to-object-storage uploads using short-lived signed URLs can reduce API-server bandwidth and improve scalability.

A webhook allows one system to notify another system when an event occurs.

A webhook endpoint should authenticate the sender, validate the payload, reject stale or malformed requests, and process events idempotently.

Webhook delivery is normally asynchronous. The sender should retry failed deliveries using an appropriate backoff strategy. The receiver should respond quickly and move expensive processing to a background queue.

Webhook signatures often use HMAC so the receiver can verify that the payload was produced by a trusted sender.

A provider may send the same event multiple times because it cannot know whether the receiver processed the first request successfully.

Store an event identifier and make processing idempotent. If the same event arrives again, return success without repeating the business side effect.

Use queues for durability, dead-letter handling for repeated failures, exponential backoff for retries, and observability for delivery latency and failure rates.