Senior US Backend Developer – Legacy PHP to Node.js Migration & Security Hardening (Flutter App)

We are looking for a senior US-based backend developer to lead a clean, secure migration of our production mobile backend from legacy PHP to Node.js. Our core product is an AI-powered clothes organizer mobile app with a Flutter frontend. Following a recent security vulnerability/exploit on our legacy PHP server, we are decommissioning the PHP backend completely and migrating our API services, database interactions, and business logic to a modern, hardened Node.js architecture. If you have extensive experience rebuilding compromised or outdated legacy backends, securing APIs, and ensuring seamless continuity for active Flutter apps, we want to hear from you. Scope of Work Legacy PHP Audit & Mapping: Review existing PHP endpoints, database queries, and business logic to prepare an efficient migration strategy. Node.js Rebuild: Reconstruct all API endpoints in Node.js (Express/Fastify/NestJS) with clean architecture and type safety. Security & Hardening: Implement strict authentication, input sanitization, rate limiting, and secure environment handling to prevent future exploits. Flutter Integration: Ensure full backward compatibility or smooth updates for our Flutter mobile app endpoints to avoid disrupting existing users. Deployment & Pipeline: Set up secure production deployment (AWS/GCP/DigitalOcean) with CI/CD and automated monitoring. Core Requirements Location: Must be based in the United States. Backend Expertise: Deep hands-on experience with Node.js, JavaScript/TypeScript, and modern API design. Legacy PHP Experience: Ability to read, understand, and extract logic from legacy PHP codebases. Security First Mindset: Strong understanding of backend security best practices, OWASP top 10, sanitization, and access control. Mobile Integration: Familiarity with Flutter/Dart frontend expectations and JSON payload structures. Engagement Details Type: Hourly contract Scope: Migration project with potential for ongoing monthly backend maintenance How to Apply When submitting your proposal, please include: Brief examples of backend migrations (especially legacy PHP to Node.js) you’ve completed. Your approach to securing endpoints during a total backend rebuild. Your current hourly rate and weekly availability.