There was tutorial on CORBA Security service during the first day of the Second Workshop on Distributed Object Computing Security given by Bret Hartman (Concept Five Technologies, Inc.).
There is a downloadable presentation in PDF format on "Security Concepts for Distributed Component Systems" By Walt Smith of Tekna, which contains an overview of the CORBASEC architecture.
This was a presentation to the 21st National Information Systems Security Conference
It is available at: http://csrc.nist.gov/nissc/1998/proceedings/tutorB2.pdf.