Worked on security hardening for the spring-projects/spring-boot repository, focusing on the NimbusJwtDecoder component. Developed a feature that enforces the use of known JWS algorithms, reducing the risk of misconfiguration and strengthening OAuth2 resource server protection. Enhanced error handling was implemented to provide clearer feedback when unknown algorithms are encountered, enabling faster remediation and improved operational guidance. The work centered on backend development using Java and the Spring Framework, with a strong emphasis on security best practices. All changes were properly documented and signed off, contributing to more robust and auditable JWT validation within the Spring Boot ecosystem.