LP1203753 AuthProxy barcode login support

When users attempt a barcode-based login with AuthProxy, the system will
determine the username of the user (based on the barcode) and use the
username instead of the barcode for all proxied login attempts.  This
allows users to use their barcodes (or barcode-looking usernames) to
log in via remote authenticators.

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Dan Wells <dbw2@calvin.edu>