PRServletContainerAuth is generally used with SSO (Single sign on) which means if users are logged into PC then there windows login will be used to log in pega. So, everytime you fetch the log in screen, it will log user in .
SSO can vary from client to client. Some client use there email ids , employee id etc as thr login.
Thanks Fahad, but in our case, we are leveraging PRServletContainerAuth for LDAP logins, so post logoff when we try to login, I would expect the system to ask for username and password like it does during first log-in attempt