Hi,
You should be able to use UserSession.getKey(). We are already using it in our remote plugin sample in order to check for some vCenter Server privileges. Please have a look at:
/samples/remote-plugin-sample/src/main/java/com/vmware/sample/remote/gateway/SessionServiceImpl.java
and
/samples/remote-plugin-sample/src/main/java/com/vmware/sample/remote/vim25/services/AuthorizationService.java
Best Regards,
Denis