The Calendar Appointment App is a web application developed using React and ASP.Net Web API, which allows multiple users to create and manage their own events, similar to Google Calendar. The app has a landing signup page, where new users can sign up for an account. When a user submits their signup details, the ASP.Net Web API handles the request and checks if the email is already registered in the in-memory database. If the email is not found, the user's details are added to the user list, and a 200 Success response is returned. If the signup fails, an error message is displayed to the user. Once the user is signed up, they can log in using their email and password. The login details are processed in the backend, where the app checks if the email and password match with the ones stored in the user table. If the authentication is successful, a custom encoded token is generated by concatenating the UUID created during signup with a new UUID generated during login. The encoded token is then set to the response header and cookie. For subsequent requests such as posting, getting, updating, or deleting calendar events, the app first checks the token's validity. It decodes the token and verifies it against the user table. If the token is valid, the actual request is processed, and the response is returned to the frontend. If the token is null or invalid, the app redirects the user to the signup page. When the user clicks the logout button, the token's value is set to null, and the cookie is updated in the response header. The app then redirects the user to the signup page. If a request is made to the backend without a valid token, the app redirects the user to the landing page, as the user must be authenticated to access the app's features.