NguyenTungs

// Ví dụ về callback truyền thống, nỗi kinh hoàng của developer.
// link ref: https://anonystick.com/blog-developer/series-callback-javascript-phan-3-async-await-la-gi-va-su-khac-nhau-giua-promise-trong-javascript-vRwGny6a.jsx
const verifyUser = function(username, password, callback){
   dataBase.verifyUser(username, password, (error, userInfo) => {
       if (error) {
           callback(error)
       }else{
           dataBase.getRoles(username, (error, roles) => {
               if (error){
                   callback(error)