如何在PHP中实现“保持登录”复选框？

Question

这是我的代码login.php，我需要一个功能保持选中状态

<?php
    session_start();

    if (isset($_SESSION["loggedin"]) && $_SESSION["loggedin"] === true) {
        header("location: welcome.php");
        exit;
    }

    require_once "config.php";

    $username     = $password = "";
    $username_err = $password_err = "";

    if ($_SERVER["REQUEST_METHOD"] == "POST") {

        if (empty(trim($_POST["username"]))) {
            $username_err = "Please enter username.";
        } else {
            $username = trim($_POST["username"]);
        }

        if (empty(trim($_POST["password"]))) {
            $password_err = "Please enter your password.";
        } else {
            $password = trim($_POST["password"]);
        }

        if (empty($username_err) && empty($password_err)) {
            $sql = "SELECT id, username, password FROM users WHERE username = ?";

            if ($stmt = mysqli_prepare($link, $sql)) {
                mysqli_stmt_bind_param($stmt, "s", $param_username);

                $param_username = $username;

                if (mysqli_stmt_execute($stmt)) {
                    mysqli_stmt_store_result($stmt);

                    if (mysqli_stmt_num_rows($stmt) == 1) {
                        mysqli_stmt_bind_result($stmt, $id, $username, $hashed_password);
                        if (mysqli_stmt_fetch($stmt)) {
                            if (password_verify($password, $hashed_password)) {

                                session_start();

                                $_SESSION["loggedin"] = true;
                                $_SESSION["id"]       = $id;
                                $_SESSION["username"] = $username;

                                header("location: welcome.php");
                            } else {
                                $password_err = "The password you entered was not valid.";
                            }
                        }
                    } else {
                        $username_err = "No account found with that username.";
                    }
                } else {
                    echo "Oops! Something went wrong. Please try again later.";
                }
            }

            mysqli_stmt_close($stmt);
        }

        mysqli_close($link);
    }
    ?>