golang gorilla session incative pop up

I am using golang to build a web backend. Framework and tools I am using are listed as follow:

1. Go http://ift.tt/1mOmNL5 as backend
2. Go http://ift.tt/1cXjCIV as session manager
3. AWS elastic cache as seesion storage

My code is list as follow

package session

import (
    "encoding/gob"
    "http://ift.tt/1L1lnVB"
    "http://ift.tt/1mOmNL5"
    "http://ift.tt/1cXjCIV"
    "log"
)

const (
    //REDIS_HOST = "test-cache.abcde.0001.use1.cache.amazonaws.com"
    REDIS_HOST  = "localhost"
    REDIS_PORT  = "6379"
    SESSION_KEY = "mypassword"
)

var Store *redistore.RediStore

type SessionType sessions.Session

func init() {
    var err error
    Store, err = redistore.NewRediStore(10, "tcp", REDIS_HOST+":"+REDIS_PORT, "", []byte(SESSION_KEY))
    if err != nil {
        log.Fatal(err)
    }
    Store.SetMaxLength(0) // NOTE: default is 4096 
    gob.Register(model.MyStruct{}
)
}

func Get(c *gin.Context, name string) *sessions.Session {
    s, err := Store.Get(c.Request, name)
    if err != nil {
        log.Println(err)
    }
    return s
}

which work perfectly in http request like follow

func Login(c *gin.Context) {
    var req map[string]string
    errBinding := c.BindWith(&req, binding.JSON)
    if errBinding != nil {
        c.JSON(400, "request format error")
        return
    }
    uid, _ := // save database get reutn id
    var _resp struct {
        Success bool `json:"success"`
        UID     int  `json:"uid"`
    }
    if uid <= 0 {
        _resp.Success = false
        _resp.UID = uid
        c.JSON(200, _resp)
        return
    } else {
        userCookie := cookie.BuildCookie(uid) //set user cookie here
        http.SetCookie(c.Writer, userCookie)
        s, _ := session.Store.Get(c.Request, "session")
        sessions := (*session.SessionType)(s)
        sessions.Values["uid"] = uid
        err := s.Save(c.Request, c.Writer)
        if err != nil {
            log.Println(err)
        }
        _resp.Success = true
        _resp.UID = uid
        c.JSON(200, _resp)
    }
}

func Logout(c *gin.Context) {
    s, _ := session.Store.Get(c.Request, "session")
    s.Options.MaxAge = -1
    s.Save(c.Request, c.Writer)
    http.SetCookie(c.Writer, &http.Cookie{
        Name:   "user",
        Path:   "/",
        Domain: ".mytest.com",
        MaxAge: -1,
    })
    c.String(200, "")
}

My problem is. I want to pop up a message to ask user to relogin, when user long time AFK or session expire? How can I catch session expire event happen? Do I need change front end, add a call that keep send call to check seesion expire or not.