CAS - Why am I being asked to input my login credential again?

If you are using the Central Authentication Service (CAS), the following are reasons why you are asked to reenter your login credential besides you explicitly logged out of CAS:

• CAS uses a cookie to determine if a user has already logged in, and the cookie expires when the user closes the browser that was used to log into CAS. So, if a user logs into CAS, and then quit their web browser, the CAS will not know who the user is, and the user will have to reenter his/her login information. Likewise, if a user uses more than one web browser, the user will have to log into CAS using each one.

  If the time limit, or session, for CAS has expired (currently 8 hours), then you will have to login again.

• You have logged into CAS, but the web application you are trying to use has asked CAS to present you with the login screen again. Web applications have the ability to ask CAS to present the login screen to the user regardless of whether or not the user has already logged in. This feature is available as an extra security precaution.