Worked on the apache/shiro repository to enhance authentication data integrity by introducing an immutable PrincipalCollection implementation in Java. Applied software architecture principles to design a builder pattern for constructing immutable collections, while deprecating the previous mutable version to eliminate mutation-related bugs. Migrated SimpleAuthenticationInfo to merge exclusively with the new immutable type, ensuring authentication flows remain deterministic and secure. Focused on improving cache integrity and reducing risks associated with in-place mutations, the changes established a safer foundation for future enhancements. Emphasized unit testing throughout development to maintain reliability and minimize runtime impact, supporting maintainability and extensibility of authentication components.