Xiaolin Talks Programming

Sep 23, 2026 · Backend Development

Spring Boot QR Code Login: State Machines, SSE Push, and Replay Protection for Production

This article details a production-ready QR code login implementation using Spring Boot, covering state machine design with Redis and Lua for atomic transitions, SSE for low-latency status push with polling fallback, HMAC-SHA256 with nonce for replay protection, and Redis Pub/Sub for cross-instance consistency in clustered deployments.