invalid indirect of oauth.RequestToken literal (type oauth.RequestToken)

为什么以下行无效？

func (s *Service) Callback(r *http.Request, req *RequestOauth, resp *Response) error {
    c := endpoints.NewContext(r)
    consumer.HttpClient=urlfetch.Client(c)
    ====>requestToken := *oauth.RequestToken{Token:req.Oauth_token, Secret:""}<======
    b, err := TwitterApi(requestToken, req.Oauth_verifier)
    resp.Message=b.Name
    return err
}

func TwitterApi(requestToken *oauth.RequestToken, verificationCode string) (u *UserT, err error) {
    accessToken, err := consumer.AuthorizeToken(requestToken, verificationCode)
    if err != nil {log.Fatal(err)}
    response, err := consumer.Get("https://api.twitter.com/1.1/account/verify_credentials.json", nil, accessToken)
    if err != nil {log.Fatal(err)}
    defer response.Body.Close()
    b, err := ioutil.ReadAll(response.Body)
    err = json.Unmarshal(b, &u)
    return
}