The potential illicit proxy is made possible by the nuance of HTTP 
whereby the requestor specifies the hostname (among other information) 
in the header of the request.  Relying upon the presenter of the service 
ticket to also specify the service identifier to check it against 
amounts to defeating the CAS feature of validating that tickets 
authenticate to the service that's actually trying to validate them.  
Any CAS client library relying on a requestor-provisioned HTTP header to 
define the service identifier will be vulnerable to a man-in-the-middle 
illicit proxy. 

So no, it is not possible to avoid the CAS-using web application's 
having to know its own service identifier, independent of information it 
is getting from presenters of CAS tickets looking to authenticate to it.

In the specific case of the Yale Java CAS Client JSP tag library, you 
set the expected service parameter value as a nested tag within the 
<cas:auth/>.

http://www.ja-sig.org/wiki/display/CASC/Using+the+CAS+JSP+tags



> Thank you Andrew.
> So, is it possible to avoid the serverName parameter by using jsp tag library 
> method of casifying an App?
>
> Thanks again.

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