Keep duplicate signed callbacks from creating duplicate supplier events
The supplier retries a valid signed callback through both old and new signing keys during overlap. Signature checks pass twice and both requests create a purchase-order update.
- Focused work estimate
- 2h 30m + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Replay prevention · Idempotency · Transactional dispatch
Estimated field mix
- Security40%
- Integrations30%
- Distributed systems30%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
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Project context
A fictional supplier integration signs incoming webhooks and uses an outbound API credential. Operators currently replace environment values by hand. Build with a deterministic secret-store adapter and fabricated keys only; no live provider account or production credential is part of the exercise.
Setup prerequisites
- Cryptographic hash APIs
- HTTP webhook handling
- Access control
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
- VAULT-101 · Inventory credential consumers without exporting their values
- VAULT-102 · Move secret lookup behind a version-aware provider
- VAULT-105 · Verify signed webhooks against raw bytes before parsing
- VAULT-103 · Redact credentials from failed supplier requests
- VAULT-104 · Model credential activation and retirement as explicit transitions
- VAULT-106 · Accept old and new webhook signatures only during a bounded overlap
Acceptance criteria
- Deduplicate by authenticated supplier event identity and tenant, independent of signing version.
- Bind the identity to a canonical payload fingerprint and conflict on changed content.
- Commit the receipt and business dispatch intent atomically.
Implementation constraints
- A valid signature proves message authenticity under the fixture protocol, not permission for duplicate side effects.
Verification to include
- Deliver the same event under both allowed keys and assert one business dispatch.
- Race duplicate callbacks and reuse the event ID with changed content; inspect stable state and conflict.
Deliverables
- Authenticated receipt deduplication and overlap replay cases
Rollout and recovery
Enable receipt uniqueness before starting overlap; retain receipts through any receiver rollback.
Value of the work
For the engineer: Practice credential lifecycle design, overlap windows, authenticated webhooks, and failure recovery without handling real secrets.
For the team: Review whether an engineer can make rotation auditable and fail closed while preserving availability and replay safety.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.