Developed the core user authentication system for the informacioni-sistem-za-aviokompanije repository, focusing on both login and registration flows. Leveraged JavaScript and axios to implement asynchronous functions that securely handle user credentials and communicate with backend API endpoints. Integrated frontend authentication logic with robust error management, ensuring users receive clear feedback during onboarding. The work established a scalable authentication layer, supporting secure access and session management for future system enhancements. Emphasized API integration and frontend development best practices throughout the process. Delivered this feature as a cohesive unit, laying the groundwork for improved user experience and maintainable authentication workflows.