Hot to get windows username from a class file in App_Code

I am hoping that this is relatively simple, but how would i go about retrieving the windows login name from the class file in the App_Code folder. I have set up my website to run windows authentication, and can use httpcontext to get windows login name from code beihind, but without passing this to the class everytime, is it possible to get the login name from within the class?
 
hope thats not too complicated to understand.
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