Worked on the spring-authorization-server repository to enhance error handling for the Device Code Flow, focusing on compliance with RFC 8628. Addressed a bug where invalidated or expired device codes did not trigger the correct OAuth2 error response, implementing logic to throw an OAuth2AuthenticationException with the INVALID_GRANT error code. Updated associated tests to ensure coverage of new edge cases and to validate the improved behavior. This backend development effort, using Java and leveraging Spring Security and OAuth2, improved interoperability and reliability for device-based clients by reducing ambiguity in client-side error handling and aligning responses with OAuth2 specifications.