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The idea is intended to reduce the need for state sharing across load balanced CAS instances.
Issues
Approach for other tickets
Ticket granting cookies are not the only tickets CAS vends. CAS also vends service tickets, proxy tickets, proxy granting tickets... When a service validates a service ticket someone presented to it, it will randomly reach one of the load balanced CAS instances. That CAS instance will need to be able to recognize and validate the service ticket. Either this same self-validating-ticket approach would need to be used to encrypt or at least sign the service identifier and other information (renewness) into the service ticket, or the CAS servers would need to share state about outstanding service tickets. Proxy tickets additionally bear an arbitrarily long chain of proxying entities, a chunk of information that would become unweildy for encrypting or signing into the proxy ticket itself.
It's hard to enforce on-time-use and revocation for self-validating tickets. That is, once you validate a service ticket it's not supposed to be re-validatable, to prevent replay attacks.