RFC // SecurityRole: Backend & Security Engineer
DisputeDrop Engine
High-integrity chargeback automation and idempotent financial webhook processor.
Production Benchmarks & Targets
Processing Guarantee
100% Exactly-Once
Distributed Redis idempotency locks
Webhook Ingestion
<45ms
Signature verification + async dispatch
Audit Integrity
Immutable
Append-only ledger event stream
System Architecture Invariants
- •Distributed idempotency keys using atomic Redis SETNX operations to prevent duplicate payment disputes.
- •Strict HMAC-SHA256 constant-time signature verification on inbound gateway webhooks.
- •Immutable audit trail with append-only PostgreSQL ledgering for forensic compliance.
Security & Threat Mitigations
- •Mitigated timing attack vectors via constant-time token comparisons.
- •Least-privilege database role mapping separating dispute submission workers from financial settlement data.
Problem & System Constraints
Payment dispute events arrive non-deterministically across payment gateways. Duplicate webhook delivery can cause duplicate dispute filings, resulting in severe gateway penalty fees.
Architectural Solution
Engineered an ingestion engine featuring strict HMAC verification, atomic idempotency caching, and an asynchronous worker pipeline that validates, aggregates evidence, and submits responses within tight gateway SLA windows.