Could you please provide all steps to reproduce?
I've just tried to deploy the spring security sample webapp of cxf 2.4.0 and 2.6.5 on Gatein 3.5.0 Final / JBOSS 7 everything works well, I could query it successfully using curl.
With Gatein 3.5.0 / JBoss 7: I can access REST service running on GateIn via Browser but throws exception when accessed via Portlet. However the same binaries works fine on JBoss Portal 2.7.2.
To reproduce it would be best to send you the Software Components and Steps. Please let me know if you are still available to help on this, and I can PM you a link with uploaded components.
Thanks for your assistance on this !