PHPはシングルユーザーログイン機能を実装します

<?php

session_start(); // 启动会话

$valid_username = "admin";
$valid_password = "password123";

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $username = $_POST["username"];
    $password = $_POST["password"];

    if ($username == $valid_username && $password == $valid_password) {
        $_SESSION["loggedin"] = true;
        echo "登录成功！";
    } else {
        echo "用户名或密码错误！";
    }
}

if (isset($_SESSION["loggedin"]) && $_SESSION["loggedin"] === true) {
    echo "欢迎回来！";
} else {
    echo "请先登录！";
}

?>

<form method="post" action="<?php echo $_SERVER["PHP_SELF"]; ?>">
    <label for="username">用户名:</label>
    <input type="text" name="username" id="username">
    <br>
    <label for="password">密码:</label>
    <input type="password" name="password" id="password">
    <br>
    <input type="submit" value="登录">
</form>