* Add ability to set authenticated user in request header
Some web applications provide the ability to authorize users based on
the authenticated from Basic Auth. This patch provides a way to set a
key to which the authenticated user can be set in the Header.
For example, if I set `HeaderValue = "X-WebAuth-User"` and authenticate,
my application will be able to read my user name from that header and
provide me with the proper access.
This fixes#802
