● Overhauled the application's security by implementing a stateless JWT architecture with Spring Security. I engineered the generation and secure rotation of tokens using RSA with PEM keys, and delivered a logout-all feature through token versioning. ● Developed the REST API for user management using Spring Boot. I implemented endpoints for account blocking and password changes, enforcing security with Role-Based Access Control (RBAC) for all administrative functions. ● Developed the logic for the user limits system (realms) using Hibernate, ensuring data integrity by implementing a transactional service layer. ● Optimized the performance of key endpoints, which reduced API response time by an average of 15% and directly improved the user experience within the application. ● Reduced critical bugs in the authentication module by 30% within 3 months through refactoring legacy code and enhancing Spring Security protocols.