Current caller subject?

[Dain Sundstrom]

I'm working on the Jencks project again and have discovered that the  
container managed security and pool partition by-subject doesn't work  
oustide of Geronimo since both depend on obtaining the current  
caller's subject from ContextManager.getCurrentCaller(), which is a  
Geronimo specific class.

Is there a spec defined way we could be getting the current caller's  
subject that would reasonably work in most app servers?  I'm hoping  
there is something in the JACC spec.  If not, I think we should  
introduce a hook under these static calls, so we can redirect them to  
platform specific APIs when running outside of a Geronimo server.

-dain