Sky Notify treats notification destinations and payloads as untrusted input.

• webhook delivery requires HTTPS
• webhook hostname must be explicitly allowlisted through NOTIFY_WEBHOOK_HOSTS
• embedded URL credentials are rejected
• redirects are not followed
• JSON payloads are bounded to 64 KiB
• optional bearer authentication uses constant-time comparison
• durable idempotency keys reduce accidental duplicate submissions
• external delivery is marked successful only after a 2xx provider response
• retry budgets transition exhausted deliveries to dead_letter
• the container runs as an unprivileged sky user
• CI performs compile, lint, tests, dependency audit, and image checks

This service does not provide SSRF-proof IP-range filtering beyond the exact hostname allowlist, tenant isolation, message encryption at rest, distributed consensus, exactly-once external delivery, or compliance certification. Operators should place it behind authenticated network boundaries, manage secrets outside the repository, back up the SQLite database, and monitor dead-letter growth.

Do not include credentials or high-value secrets in notification payloads unless the deployment adds an appropriate encrypted storage and data-handling layer.