Get the identity of the current user in a class

In a .aspx page, I can get the identity of the current user with:

Dim CurrentUser as string = User.Identity.Name

In a class (for example, MyClass.vb), User,Identity.Name gives the error:

"User" is not declared.  It may be inaccessible due to its protection level.

I've tried importing Microsoft. VisualBasics.ApplicationServices to no avail.

Your help would be much appreciated.

Thanking you in anticipation.

Roger