auth - middleware update

const promiseMiddleware = store => next => action => {
  // if the action's payload is a promise, trigger this middleware
  if (isPromise(action.payload)) {
    // trigger UI's loading state
    store.dispatch({ type: 'ASYNC_START', subtype: action.type });
    // let promise succeed/fail
    action.payload.then(
      // if it succeeds, mutate payload into the promised data and
      // dispatch action to store
      res => {
        action.payload = res;
        store.dispatch(action);
      },
      // failure => set an error flag on action and mutate payload into
      // the error message. dispatch action to store
      error => {
        action.error = true;
        action.payload = error.response.body;
        store.dispatch(action);
      }
    );

    return;
  }

  // if the action payload is not a promise, send the action over to the next middleware
  // or dispatch it to the store if this is the last middleware in the chain
  next(action);
}

function isPromise(v) {
  return v && typeof v.then === 'function';
}

export {
  promiseMiddleware
};