docs: def login(self, action, registry, **kwargs):
          """
          Logs in to a Docker registry.
  
          :param action: Action configuration.
          :type action: dockermap.map.runner.ActionConfig
          :param registry: Name of the registry server to login to.
          :type registry: unicode | str
          :param kwargs: Additional keyword arguments to complement or override the configuration-based values.
          :type kwargs: dict
          """
          log.info("Logging into registry %s.", registry)
          login_kwargs = {'registry': registry}
          auth_config = action.client_config.auth_configs.get(registry)
          if auth_config:
              log.debug("Registry auth config for %s found.", registry)
              login_kwargs.update(auth_config)
              insecure_registry = kwargs.get('insecure_registry')
              if insecure_registry is not None:
                  login_kwargs['insecure_registry'] = insecure_registry
          else:
              raise KeyError("No login information found for registry.", registry)
          update_kwargs(login_kwargs, kwargs)
          res = action.client.login(**login_kwargs)
          if res:
              log.debug("User %(username)s logged into %(registry)s.", login_kwargs)
              self._login_registries.add(registry)
          return res