How to use session with golang revel framework

I use the golang web framework as my web framework. But the session doesn`t use. the code I write as follow :

package controllers 

import (
    "fmt"
    "net/http"
    "strconv"

    "GoRBAC/app/base"
    "GoRBAC/app/models"

    r "http://ift.tt/1lwG43h"
)

type App struct {
    *r.Controller
}

// 首页
func (this App) Index() r.Result {
    userDao := models.NewUserDao()
    user, err := userDao.QueryById(1)
    if err != nil {
        fmt.Println(err)
    }
    fmt.Println(user)
    return this.Render()
}

// 跳转至登录页面
func (this App) ToLogin() r.Result {
    return this.RenderTemplate("App/login.html")
}

func (this App) Login() r.Result {

    username := this.Params.Get("username")
    password := this.Params.Get("password")
    securityCode := this.Params.Get("securityCode")

    fmt.Println(this.Session["securityCode"])
    fmt.Println(username)
    fmt.Println(password)
    fmt.Println(securityCode)

    if securityCode != this.Session["securityCode"] {
        return this.RenderText("error securityCode")
    } else {
        userDao := models.NewUserDao()
        user, err := userDao.QueryByUsername(username)
        if err != nil || user == nil {
            return this.RenderText("username not exsit")
        } else if user.Password != password {
            return this.RenderText("error password")
        } else {
            delete(this.Session, "securityCode")
            this.RenderText("ok")
        }
    }
    return this.RenderText("ok")
}

// 获取验证码图片
func (this App) GetSecurityCode(timestamp int64) r.Result {
    // 时间戳参数，第一次加载为1，后续加载为当前的时间戳，可以用来验证客户端刷新频率
    // 如：刷新频率过高，直接限制当前客户端等
    fmt.Println("GetSecurityCode", timestamp)

    d := make([]byte, 4)
    s := base.NewLen(4)
    ss := ""
    d = []byte(s)

    for v := range d {
        d[v] %= 10
        ss += strconv.FormatInt(int64(d[v]), 32)
    }

    // 将验证码字符串存入到session
    this.Session["securityCode"] = ss
    this.Session.SetNoExpiration()

    fmt.Println(this.Session["securityCode"])
    fmt.Println(ss)

    this.Response.Status = http.StatusOK
    this.Response.ContentType = "image/png"

    base.NewImage(d, 100, 40).WriteTo(this.Response.Out)

    return this.Render()
}

I set the securityCode value in session in the method GetSecurityCode() , this method use to generate the security Code for login verify

I use the the securityCode value in the method Login(). But I get nothing for the value

Anyone who can help me , how can I fix this problem ?

thanks !!