Worked on backend development for the cBioPortal/cbioportal repository, focusing on enhancing API security through Spring Security. Addressed a critical bug by reordering the Spring Security filter chains so that the API security chain executes before the OAuth2 filter chain, ensuring that authentication and authorization for API requests are handled in the correct sequence. This adjustment reduces the risk of misrouted authentication flows and maintains proper authorization sequencing. The solution was implemented in Java and delivered as a single, auditable commit, reflecting a precise and targeted approach to security hardening within the existing backend infrastructure using established Spring Security practices.