docs: def get_default_plugin(cls):
          '''
          Return a default plugin.
          '''
          from importlib import import_module
          from django.conf import settings
          default_plugin = getattr(settings, 'ACCESS_DEFAULT_PLUGIN', "access.plugins.DjangoAccessPlugin")
          if default_plugin not in cls.default_plugins:
              logger.info("Creating a default plugin: %s", default_plugin)
              path = default_plugin.split('.')
              plugin_path = '.'.join(path[:-1])
              plugin_name = path[-1]
              DefaultPlugin = getattr(import_module(plugin_path), plugin_name)
              cls.default_plugins[default_plugin] = DefaultPlugin()
          return cls.default_plugins[default_plugin]