Worked on the envoyproxy/envoy repository to deliver a resilient OAuth2 enhancement for the Envoy proxy, focusing on backend and API development using C++. Developed an 'allow_failed_matcher' feature within the OAuth2 filter, enabling requests to proceed upstream as unauthenticated when OAuth validation fails, while stripping OAuth cookies and adding informative headers. This approach allows services to handle both authenticated and unauthenticated requests gracefully, reducing upstream errors and aligning with existing JWT filter patterns. Comprehensive unit tests were implemented to ensure coverage of various failure scenarios, and documentation, changelogs, and release notes were updated to support release readiness and maintainability.