How to import httpcontext.current into VB class file

From my code behind files I can set session variables just by typing something like:
session("whatever") = True
However, I have a VB class file called Engine.vb where I'm trying to do the same thing, but it's not working.  To get it to work, I have to type something like:
HttpContext.Current.Session("whatever") = True
Is there a way that I can import all of HttpContext.Current so I don't have to type HttpContext.Current everytime.  Why does this even happen here if it doesn't happen in the code behind files?
Thanks
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