Fixed bug with authentication with a plain password.

            return None

        is_valid = False

        m = CCConf.RE_SALTPW.match(passwd_conf)

        if m is None:

            is_valid = self._auth_plain(passwd_conf, password)

            meth = '_auth_plain'

            password_wo_method = passwd_conf

        else:

            meth = '_auth_%s' % m.group('method').lower()

            password_wo_method = m.group('password')

        if hasattr(self, meth):

            auth = getattr(self, meth)

                is_valid = auth(password, m.group('password')) == passwd_conf

            is_valid = auth(password, password_wo_method) == passwd_conf

        else:

            logging.warning('Bad authentication method for %s: '

                            '%s' % (login, m.group('method')))