Senior Node.js/TypeScript Engineer — Security Hardening & Launch Readiness (Sports Data Platform)

We run a real-time sports data platform (live scores, statistics and odds context for professional tennis) with a mobile app heading into public launch. An external code review has given us a clear, prioritized list of what needs hardening first. We're hiring one senior engineer to own the highest-risk items and get us release-ready. Our stack: - Flutter mobile app (recently redesigned) - Node.js / TypeScript / Express backend API - MongoDB Atlas - Python data-collection and monitoring services (Docker, Railway, AWS) - Firebase What you'd own (part-time, roughly 10-20 hrs/week, est. 2-3 months): - Backend security hardening: consistent authentication/authorization across routes, ownership validation on user-specific operations, secrets management - Replacing process-local caching with a shared caching layer; reducing heavy client polling load - CI/CD: staging environment, baseline regression tests, secret scanning, deploy automation and rollback - Production observability: centralized logging, monitoring, crash reporting - Reviewing security-relevant changes produced by our in-house team How we work: you'll collaborate directly with our in-house full-stack developer who knows the codebase deeply, and we use AI-assisted development heavily. Your leverage here is senior judgment, architecture and review — owning the hardest 20%, not carrying volume. You're a fit if you have: - 5+ years with Node.js/TypeScript in production - Real experience hardening and operating production APIs (auth, caching, rate limiting) - AWS + Docker + CI/CD experience; infrastructure-as-code is a plus - Experience taking over an existing codebase and improving it progressively, without rewriting - Clear written communication NDA required before repository access — we work with sanitized review snapshots first. To apply, briefly describe one production system you hardened or took over: what you found, what you fixed first, and why.