code: def _request_auth(self, registry):
          
          if registry:
              if registry.auth:
                  registry.auth.load_dockercfg()
  
              try:
                  self._client_session.login(username=registry.auth.user,
                                             password=registry.auth.passwd,
                                             dockercfg_path=registry.auth.config_path,
                                             reauth=True if registry.auth.auth_type == 'registry_rubber' else False,
                                             registry=registry.auth.registry)
              except Exception:
                  raise
          else:
              raise Exception("a registry is required when requesting auth.")
docs: self, username, password=None, email=None, registry=None,
                reauth=False, insecure_registry=False, dockercfg_path=None):