This module provides methods for authenticating a user.
       It uses HTTPD::UserAdmin to lookup passwords in a
       database.  Subclasses provide methods specific to the
       authentication mechanism.

       Currently, under HTTP/1.0 the only supported
       authentication mechanism is Basic Authentication.  NCSA
       Mosaic and NCSA HTTPd understand the proposed Message
       Digest Authentication, which should make it into the HTTP
       spec someday.  This module supports both.