I'm totally stumped on this one. It's not as easy as it first sounds.

Code:
SELECT SYSTEM_USER;
The above returns login name but the problem is when an SQL login uses windows authentication and is mapped to a user group. Thus, my login name is "MyDomain\Domain Admins" but the above function returns: "MyDomain\simon_m".

How can I possibly determine what the actual SQL login used was for the current connection?

Background: I need to do this because I want to assess whether the current connection is able to VIEW SERVER STATE (which is a server permission). If I can pin down which login I am, I can work it out. But if anyone has any alternatives, I am open to suggestions?