try:

            plugin = loadplugin(module)

        except (ImportError, AttributeError, TypeError), e:

            raise ImportError('Failed to load authentication module %s : %s'

                              % (module, str(e)))

        log.debug('Trying authentication using ** %s **' % (module,))

        # load plugin settings from Kallithea database

        plugin_name = plugin.name

        plugin_settings = {}

        for v in plugin.plugin_settings():

            conf_key = "auth_%s_%s" % (plugin_name, v["name"])

            setting = Setting.get_by_name(conf_key)

            plugin_settings[v["name"]] = setting.app_settings_value if setting else None

        log.debug('Plugin settings \n%s' % formatted_json(plugin_settings))

        if not str2bool(plugin_settings["enabled"]):

            log.info("Authentication plugin %s is disabled, skipping for %s"

                     % (module, username))

            continue

        # use plugin's method of user extraction.

        user = plugin.get_user(username, environ=environ,

                               settings=plugin_settings)

        log.debug('Plugin %s extracted user is `%s`' % (module, user))

        if not plugin.accepts(user):

            log.debug('Plugin %s does not accept user `%s` for authentication'

                      % (module, user))

            continue

        else:

            log.debug('Plugin %s accepted user `%s` for authentication'

                      % (module, user))

        log.info('Authenticating user using %s plugin' % plugin.__module__)

        # _authenticate is a wrapper for .auth() method of plugin.

        # it checks if .auth() sends proper data. for KallitheaExternalAuthPlugin

        # it also maps users to Database and maps the attributes returned

        # from .auth() to Kallithea database. If this function returns data

        # then auth is correct.

        plugin_user = plugin._authenticate(user, username, password,

                                           plugin_settings,

                                           environ=environ or {})

        log.debug('PLUGIN USER DATA: %s' % plugin_user)

        if plugin_user:

            log.debug('Plugin returned proper authentication data')

            return plugin_user

        # we failed to Auth because .auth() method didn't return proper the user

        log.warning("User `%s` failed to authenticate against %s"

                    % (username, plugin.__module__))

    return None