Application owners who do not wish to use Single Sign-On for a particular application can force the browser to request credentials for CAS even if the browser has been previously authenticated. This is called renew, and the feature is outlined in section 2.1.1. parameters of the CAS documentation on the CAS Protocol.
To set your application to require re-authentication and to present the CAS login screen for browsers regardless of whether or not the browser has been already authenticated, answer Yes next to the question Requires Reauthentication on the CAS Registration form.