PHP登录并记住我

Question

晚上，

我在做饼干的噩梦。我尝试了100万种方法来保持用户登录但失败。

我的login.php

<?php
require_once('config.php');
if( $user->is_logged_in() ){ header('Location: index.php'); exit(); }
if(isset($_POST['submit'])){
    if (!isset($_POST['username'])) $error[] = "Please fill out all fields";
    if (!isset($_POST['password'])) $error[] = "Please fill out all fields";
    $username = $_POST['username'];
    if ( $user->isValidUsername($username)){
        if (!isset($_POST['password'])){
            $error[] = 'A password must be entered';
        }
        $password = $_POST['password'];
        if($user->login($username,$password)){
            $_SESSION['username'] = $username;
            header('Location: index.php');
            exit;
        } else {
            $error[] = 'Wrong username or password or your account has not been activated.';
        }
    }else{
        $error[] = 'Usernames are required to be Alphanumeric, and between 3-16 characters long';
    }
}
?>

以及在页面顶部当前需要使用用户登录的页面上。

if( $user->is_logged_in() ){ header('Location: profile.php'); exit(); }

关于如何向现有脚本添加cookie的任何建议？我不太擅长PHP，因此需要一些基本但安全的东西。谢谢大家！