An extension of the form authenticator that associates the j_username with
the session under the attribute name j_username for use by form login/error
pages.
An Authenticator and Valve implementation of FORM BASED
Authentication, as described in the Servlet API Specification, Version 2.2.
The refactored FormAuthenticator suggested in
http://issues.apache.org/bugzilla/show_bug.cgi?id=36136
author: Craig R.
An abstract subclass of UsernamePasswordLoginModule that makes the
HttpServletRequest from the client attempting to login available to the Login
Module.