How to pass multiple values in cookie with map

Got stuck while passing multiple values in cookie. I'm not able to find a better way for managing session and cookies. Trying to use github.com/gorilla/securecookie this package.
<h3>loginMain.go</h3>
package main

import (
"database/sql"
"log"
"net/http"
"shambhavi/packages/loginPkg"   
_ "github.com/go-sql-driver/mysql"
"github.com/gorilla/mux"
)
var router = mux.NewRouter()
var db *sql.DB
func connectDb() *sql.DB {
db, dberr := sql.Open("mysql", "root:root@tcp(127.0.0.1:8889)/shambhavi_db")
if dberr != nil {
log.Println(dberr)
}
return db
}
func login(w http.ResponseWriter, r *http.Request) {
var db *sql.DB = connectDb()
loginPkg.LoginOperation(w, r, db)
}
func main() {
http.HandleFunc("/demo", login)
http.Handle("/", router)
err := http.ListenAndServe(port, nil) // setting listening port
if err != nil {
log.Fatal("ListenAndServe: ", err)
}
}  

<h3>LoginPkg.go</h3>

package loginPkg
import (
"database/sql"
"encoding/json"
"fmt"
"net/http"
"shambhavi/packages/sessionPkg"
_ "github.com/go-sql-driver/mysql"
)
var retMap = make(map[string]string)
func ErrorHandler(err error) {
if err != nil {
panic(err)
}
}
func LoginOperation(w http.ResponseWriter, r *http.Request, db *sql.DB) {
fmt.Println("In LoginOperation ")
r.ParseForm()
if len(r.Form["username"][0]) == 0 && len(r.Form["password"][0]) == 0 {
fmt.Fprintf(w, "Something is blank !!!")
} else {
var lvl string
var uFullName string
err := db.QueryRow("SELECT lvl_flag FROM admin_instance WHERE user_name = ? AND passwd = ?", r.FormValue("username"), r.FormValue("password")).Scan(&lvl)
er := db.QueryRow("SELECT emp_name FROM emp_detail WHERE emp_uname = ?", r.FormValue("username")).Scan(&uFullName)
ErrorHandler(er)
retMap["msg"] = "Login successfully"
retMap["err"] = "Not Login"
retMap["lvl"] = lvl
retMap["fullName"] = uFullName
b, _ := json.Marshal(retMap)
if err != nil {
fmt.Println(err)
fmt.Fprintf(w, "%s", b)
} else {
if lvl == "1" || lvl == "2" || lvl == "3" {
sessionPkg.SetSession(w, r, r.FormValue("username"), retMap) // Passing map to the fun, retMap
fmt.Fprintf(w, "%s", b)
usrnm := sessionPkg.GetUserName(r)
fmt.Println("From session variable", usrnm)
} else {
fmt.Println("Chukala ....")
fmt.Fprintf(w, "%s", b)
}	
}
}
defer db.Close()
}

The problem lies in following file....
<h3>sessionHandler.go</h3>

package sessionPkg
import (
"fmt"
"net/http"
"time"
"github.com/gorilla/securecookie"
)
var cookieHandler = securecookie.New(
securecookie.GenerateRandomKey(64),
securecookie.GenerateRandomKey(32))
func SetSession(w http.ResponseWriter, r *http.Request, username string, retMap map[string]string) {
sessionData := map[string]string{
"userName": username,
"lvl":      retMap["lvl"],
"fullName": retMap["fullName"],
}
expiration := time.Now().Add(365 * 24 * time.Hour)
//if encoded, err := cookieHandler.Encode("session", sessionData); err == nil {
cookie := http.Cookie{
Name:    "session",
Value:   sessionData["userName"], //Here i want map or something else that can accept multiple values
Expires: expiration,
//MaxAge: 3600,
}
http.SetCookie(w, &cookie)
//}
}
func GetUserName(request *http.Request) (userName string) {
//fmt.Println(request.Cookie("session"))
cookieValue := make(map[string]string)
if cookie, err := request.Cookie("session"); err == nil {
fmt.Println("cookieValue = ", cookie.Value)
//if err = cookieHandler.Decode("session", cookie.Value, &cookieValue); err == nil {
//fmt.Println(cookie)
cookieValue["userName"] = cookie.Value
//fmt.Println(cookieValue["userName"])
//}
/*else {
fmt.Println("Error ", err)
}*/
}
return cookieValue["userName"]
}
/*func GetFullName(request *http.Request) (fullName string) {
fmt.Println("In GetFullName")
cookieValue := make(map[string]string)
if cookie2, err := request.Cookie("session"); err == nil {
fmt.Println("cookieValue = ", cookie2.Value)
//if err = cookieHandler.Decode("session", cookie.Value, &cookieValue); err == nil {
fmt.Println(cookie2)
cookieValue["fullName"] = cookie2.Value
fmt.Println(cookieValue["fullName"])
//}
}
return cookieValue["fullName"]
}*/
func ClearSession(response http.ResponseWriter) {
cookie := &http.Cookie{
Name:   "session",
Value:  "",
Path:   "/",
MaxAge: -1,
}
http.SetCookie(response, cookie)
}

Problem indicated in code by comment. I want to use session like in PHP. Suggest the better way to secure the cookie and maintain the session. Give some explanation too.

Edited: Explain cookieHandler.Encode() and cookieHandler.Decode(). It is not decoding the data which is passed to it.

• var retMap = make(map[string]string) is a global map that you both read and write to, which is unsafe: when you have more than one user concurrently you will be overwriting the contents of this map.

• You aren't using the securecookie package to encode your cookie values at all - in fact it's not clear where you're using it at all.

    cookie := http.Cookie{
  Name:    "session",
  // This should be encoded.
  Value:   sessionData["userName"], //Here i want map or something else that can accept multiple values
  Expires: expiration,
  //MaxAge: 3600,
  }
  

• Too many packages: you have a loginpackage, a sessionpackage and a package main. Packages should fulfil a 'theme' - an auth package might make more sense, or even just a single package main until you get more familiar with Go.

• You're not hashing your passwords - storing the plain text password in the database and looking it up with the value of r.FormValue("password") is extremely insecure. Read this to see how to hash passwords safely in Go: https://stackoverflow.com/questions/18545676/golang-app-engine-securely-hashing-a-users-password

• You should be using the gorilla/sessions package rather than the lower-level securecookie package.

Modifying the gorilla/sessions example in the documentation:

package main
import (
"net/http"
"github.com/gorilla/sessions"
)
// Use the CookieStore
var store = sessions.NewCookieStore([]byte("something-very-secret"))
func LoginOperation(w http.ResponseWriter, r *http.Request) {
// Your existing DB code - shorter to make the example here clearer
err := db.QueryRow("SELECT lvl_flag FROM admin_instance WHERE user_name = ? AND passwd = ?", r.FormValue("username"), r.FormValue("password")).Scan(&lvl)
// Don't use a global map - create a new one
userDetails := make(map[string]string)
userDetails["msg"] = "Login successfully"
userDetails["err"] = "Not Login"
userDetails["lvl"] = lvl
userDetails["fullName"] = uFullName
// Get a session (existing/new)
session, err := store.Get(r, "session-name")
if err != nil {
http.Error(w, err.Error(), 500)
return
}
// Set some session values.
session.Values["userDetails"] = userDetails
// Save it before we write to the response/return from the handler.
session.Save(r, w)
}

Later, if you want to retrieve the details:

func RequireAuth(w http.ResponseWriter, r *http.Request) {
// Get a session (existing/new)
session, err := store.Get(r, "session-name")
if err != nil {
http.Error(w, err.Error(), 500)
return
}
// Type assert our userDetails map out of the session's map[string]interface{}
userDetails, ok := session.Values["userDetails"].(map[string]string)
if !ok {
// User does not have an existing session - treat them as not logged in and/or re-direct them to your login page.
http.Error(w, http.StatusCode(401), 401)
return
}
// Check the user details - e.g. if userDetails["lvl"] == "ACTIVE" { ... }
// TODO
}