PHP 및 XML: 사용자 로그인 및 권한 관리 구현 방법

<form action="login.php" method="post">
    <label for="username">用户名：</label>
    <input type="text" name="username" id="username" required><br>
    <label for="password">密码：</label>
    <input type="password" name="password" id="password" required><br>
    <input type="submit" value="登录">
</form>

<?php
    // 从表单中获取用户名和密码
    $username = $_POST['username'];
    $password = $_POST['password'];
    
    // 使用XML文件验证用户身份
    $xml = simplexml_load_file('users.xml');
    $user = $xml->xpath("/users/user[username='$username' and password='$password']");
    
    if ($user) {
        // 登录成功
        session_start();
        $_SESSION['username'] = $username;
        header("Location: dashboard.php");
    } else {
        // 登录失败
        echo "用户名或密码错误";
    }
?>

<users>
    <user>
        <username>admin</username>
        <password>admin123</password>
    </user>
    <user>
        <username>guest</username>
        <password>guest123</password>
    </user>
</users>

<?php
    session_start();
    
    if (!isset($_SESSION['username'])) {
        // 用户未登录，跳转到登录页面
        header("Location: login.php");
    }
    
    // 验证用户权限
    $xml = simplexml_load_file('users.xml');
    $user = $xml->xpath("/users/user[username='".$_SESSION['username']."']");
    $role = $user[0]->role;
    
    if ($role != 'admin') {
        // 用户没有管理员权限，跳转到无权限页面
        header("Location: no_access.php");
    }
?>

<?php
    // 更新用户权限
    $xml = simplexml_load_file('users.xml');
    $user = $xml->xpath("/users/user[username='new_user']");
    
    if ($user) {
        $user[0]->role = 'admin';
        $xml->asXML('users.xml');
        echo "用户权限已更新";
    } else {
        echo "未找到用户";
    }
?>