AUTH_USER blank when using HttpContext.Current

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I have an application that uses Forms Authentication in connection with
Active Directory for granting access to an application. When a user logs on
with AD, it populates the AUTH_USER ServerVariable and I can then use:

Request.ServerVeriables["AUTH_USER"]

to retrieve the value of this variable or any other value in the
ServerVariableCollection.
A problem occurs when from an external class reference I use the following

HttpContext.Current.Request.ServerVeraibes["AUTH_USER"]

The value is always blank. If Im requesting the Current context of the
application referring the class, why is it blank. Other server values in the
ServerVariable collection are accessible both internal and externally. Why
not this one? If I request the variable both before creating the external
class reference and after its completed, its there.

--
JP
..NET Software Developer