During a two-month period, Lucky Zhang enhanced authentication and concurrency mechanisms in the spring-framework and alibaba/nacos repositories using Java and the Spring Framework. In spring-framework, Lucky refactored the ResponseBodyEmitter to use AtomicBoolean for thread-safe signaling, addressing race conditions in concurrent streaming scenarios. For alibaba/nacos, Lucky implemented automatic token refresh and re-login logic to maintain seamless client-server communication, and later introduced randomized token refresh windows to distribute login traffic and reduce server load. These contributions demonstrated depth in backend development, error handling, and server management, resulting in more robust, scalable authentication flows and improved reliability for high-traffic environments.