GSS names are not user names

[nicowilliams]

Calling the client principal name a "username" is problematic. When I started looking at this I immediately feared there might be post-processing of the name to truncate any @REALM portions.

The API should provide access to the displayed and exported name forms for the initiator and acceptor names, and possibly a wrapper for the gss_name_t values themselves so that name attributes can be accessed.