CASC-189 : Handle authentication date returned by custom CAS 2.0 service ticket validation

To add CAS remember-me support in Spring Security (based on time between authentication creation date and now) : https://github.com/SpringSource/spring-security/pull/14, we now handle authentication date from SAML response.

For CAS proxy service (as we don't have SAML validation), I propose to handle authentication date from CAS 2.0 service ticket validation response if the custom extra attribute <cas:authentiationDate> is used.