Here is the Scenario
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Q: How do I bypass the unauthenticated page if I already have a CAS ticket?
A: The CAS Server includes a feature whereby you can set the request parameter "gateway" to "true" on the request for CAS login. If "gateway" is "true", then CAS will not paint the user login screen. If it can accomplish authentication by single sign on - that is, by detecting the CAS ticket granting cookie - then it will redirect to the URL specified by the "service" parameter with a valid service ticket. If it cannot accomplish single sign on, then it will redirect to the "service" URL without painting any login screen.
In your CAS web.xml file you would include the following snippet. Notice the gateway is set to true.
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