High-level CAS authentication flow

At a high level, CAS is composed of a CAS server, which is the central web application for determining authentication, and one or more CAS services, which are distinct web applications that use the CAS server to get authenticated. The basic authentication flow of CAS proceeds via the following actions:

1. The user attempts to access a protected resource on the website.
2. The user is redirected through the browser from the CAS service to the CAS server to request a login.
3. The CAS server is responsible for user authentication. If the user is not already authenticated to the CAS server, it requests credentials from the user. In the following diagram, the user is presented with a login page.
4. The user submits the credentials (that is, the username and password).
5. If the user's credentials are valid, the CAS server responds with a redirect through...