You need an account for the API. You can't access the API anonymously. It's designated that schools give each student a user account for the WebUntis server they're using. Many schools just make the ...

project-root/ ├── core/ # Shared logic for WebUntis + iCal generation │ ├── webuntisAuth.js # Login/auth against WebUntis API │ ├── domain.js # Resolve and validate WebUntis host domain │ ├── ...