How to use the taskcluster-client-web.Auth function in taskcluster-client-web

if (action.kind === 'task') {
      context.task = task;
      context.ownTaskId = actionTaskId;
      const actionTask = jsone(action.task, context);
      const decisionTask = await queue.task(decisionTaskId);
      const submitQueue = queue.use({ authorizedScopes: decisionTask.scopes });

      await submitQueue.createTask(actionTaskId, actionTask);

      return actionTaskId;
    }

    if (action.kind === 'hook') {
      const hookPayload = jsone(action.hookPayload, context);
      const { hookId, hookGroupId } = action;
      const auth = new Auth({ rootUrl: currentRepo.tc_root_url });

      const userCredentials = testMode
        ? taskcluster.getMockCredentials()
        : taskcluster.getCredentials(currentRepo.tc_root_url);
      if (!userCredentials) {
        throw new Error(tcCredentialsMessage);
      }
      const hooks = new Hooks({
        rootUrl: currentRepo.tc_root_url,
        credentials: userCredentials.credentials,
      });
      const decisionTask = await queue.task(decisionTaskId);
      const expansion = await auth.expandScopes({
        scopes: decisionTask.scopes,
      });
      const expression = `in-tree:hook-action:${hookGroupId}/${hookId}`;