Worked on the grpc/grpc-go repository to enhance security and reliability in XDS RBAC authentication. Addressed a potential authorization bypass by implementing a strict presence-based short-circuit in the authenticatedMatcher, ensuring only the first non-empty identity source—URI SAN, DNS SAN, or Subject DN—is used, in line with gRFC A41 and Envoy specifications. Updated the matching logic in Go to enforce this order and added comprehensive regression tests to validate the new behavior and prevent future regressions. Documented the changes with detailed release notes, demonstrating a focus on backend development, security best practices, and robust testing methodologies throughout the process.