Worked on enhancing security and reliability in the spring-security and spring-boot repositories, focusing on authentication and backend stability using Java, Spring Boot, and Spring Security. Delivered improvements to JWT authentication by refactoring authority extraction logic, removing unnecessary configuration, and adding null-safety checks to prevent runtime exceptions. Addressed a bug in data source initialization by introducing a null check for the driver property, ensuring robust handling of edge cases. Expanded unit test coverage to validate these changes, increasing confidence in deployment. The work emphasized runtime safety, reduced configuration complexity, and improved developer experience through targeted, well-tested backend enhancements.