func Authenticator(r *ghttp.Request) (interface{}, error) {
	var (
		apiReq     *model.ApiLoginReq
		serviceReq *model.ServiceLoginReq
	)
	if err := r.Parse(&apiReq); err != nil {
		return "", err
	}
	if err := gconv.Struct(apiReq, &serviceReq); err != nil {
		return "", err
	}
	
	// user {"id": 1, "username": "admin"}
	if user := service.User.GetUserByUsernamePassword(serviceReq); user != nil {
		return user, nil
	}

	return nil, jwt.ErrFailedAuthentication
}

// LoginResponse is used to define customized login-successful callback function.
func LoginResponse(r *ghttp.Request, code int, token string, expire time.Time) {
	r.Response.WriteJson(g.Map{
		"code":   http.StatusOK,
		"token":  token,
		"expire": expire.Format(time.RFC3339),
	})
	r.ExitAll()
}

func RefreshResponse(r *ghttp.Request, code int, token string, expire time.Time) {
	r.Response.WriteJson(g.Map{
		"code":   http.StatusOK,
		"token":  token,
		"expire": expire.Format(time.RFC3339),
	})
	r.ExitAll()
}

func LogoutResponse(r *ghttp.Request, code int) {
	r.Response.WriteJson(g.Map{
		"code":    code,
		"message": "success",
	})
	r.ExitAll()
}

func Unauthorized(r *ghttp.Request, code int, message string) {
	r.Response.WriteJson(g.Map{
		"code": code,
		"msg":  message,
	})
	r.ExitAll()
}

// PayloadFunc is a callback function that will be called during login.
// Using this function it is possible to add additional payload data to the webtoken.
// The data is then made available during requests via c.Get("JWT_PAYLOAD").
// Note that the payload is not encrypted.
// The attributes mentioned on jwt.io can't be used as keys for the map.
// Optional, by default no additional data will be set.
func PayloadFunc(data interface{}) jwt.MapClaims {
	claims := jwt.MapClaims{}
	params := data.(map[string]interface{})
	if len(params) > 0 {
		for k, v := range params {
			claims[k] = v
		}
	}
	return claims
}

// IdentityHandler get the identity from JWT and set the identity for every request
// Using this function, by r.GetParam("id") get identity
func IdentityHandler(r *ghttp.Request) interface{} {
	claims := jwt.ExtractClaims(r)
	return claims[Auth.IdentityKey]
}