Developed and delivered WebSocket cookie-based authentication for the lightpanda-io/browser repository, enabling secure access to session-gated WebSocket endpoints. The work involved implementing cookie handling in JavaScript, ensuring that session cookies from the session jar are correctly applied to WebSocket upgrade requests in compliance with RFC 6455 and RFC 6265. Added comprehensive tests using a custom TestWSServer fixture to verify that cookies are sent and received during the upgrade process, thereby expanding test coverage. Focused on session management, testing, and WebSocket development, the changes improved compatibility with protected endpoints and enhanced the end-to-end authentication flow for users.