CAS is a Single SignOn solution. Internally the function of CAS is to create, update, and delete a set of objects it calls "Tickets" (a word borrowed from Kerberos). A Logon Ticket object is created to hold the Netid when a user logs on to CAS. A partially random string is generated to be the login ticket-id and is sent back to the browser as a Cookie and is also used as a "key" to locate the logon ticket object in a table. Similarly, CAS creates Service Tickets to identity a logged on user to an application that uses CAS authentication.
CAS data or "state" only consists of its configuration parameters, its saved tickets, and a temporary "flow" state maintained between the time it writes the login form to the screen and the time the user submits a userid and password. Ticket objects are the only important data to save, restore, or share.
A standalone CAS server stores ticket objects in memory, but when you add a second CAS server to the network for reliability, then you have to share the ticket objects either by sharing tables in a database or by configuring one of several packages that replicate Java objects over a network.
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