PHPで安全かつ信頼性の高いメール認証ログイン登録機能を実装するにはどうすればよいですか?

<?php
// 连接数据库
$servername = "localhost";
$username = "yourusername";
$password = "yourpassword";
$dbname = "yourdatabasename";
$conn = new mysqli($servername, $username, $password, $dbname);

// 获取注册表单提交的数据
if(isset($_POST['email']) && isset($_POST['password'])) {
    $email = $_POST['email'];
    $password = $_POST['password'];

    // 生成随机验证码
    $verification_code = substr(md5(rand()), 0, 8);

    // 将用户的数据插入数据库
    $sql = "INSERT INTO users (email, password, verification_code) VALUES ('$email', '$password', '$verification_code')";
    $result = $conn->query($sql);

    if($result) {
        // 发送验证邮件
        $to = $email;
        $subject = "邮箱验证";
        $message = "请点击以下链接完成验证：http://example.com/verify.php?code=$verification_code";
        $headers = "From: webmaster@example.com";
        mail($to, $subject, $message, $headers);

        echo "注册成功，请登录您的邮箱进行验证。";
    } else {
        echo "注册失败，请重试。";
    }
}

// 关闭数据库连接
$conn->close();
?>

<?php
// 连接数据库
$servername = "localhost";
$username = "yourusername";
$password = "yourpassword";
$dbname = "yourdatabasename";
$conn = new mysqli($servername, $username, $password, $dbname);

// 获取验证链接中的验证代码
$verification_code = $_GET['code'];

// 查找匹配的用户记录
$sql = "SELECT * FROM users WHERE verification_code = '$verification_code'";
$result = $conn->query($sql);

if($result->num_rows > 0) {
    // 更新用户的验证状态
    $sql = "UPDATE users SET verified = 1 WHERE verification_code = '$verification_code'";
    $conn->query($sql);

    echo "验证成功！请返回登录页面并登录。";
} else {
    echo "验证失败，请重新尝试或联系管理员。";
}

// 关闭数据库连接
$conn->close();
?>

<?php
// 连接数据库
$servername = "localhost";
$username = "yourusername";
$password = "yourpassword";
$dbname = "yourdatabasename";
$conn = new mysqli($servername, $username, $password, $dbname);

// 获取登录表单提交的数据
if(isset($_POST['email']) && isset($_POST['password'])) {
    $email = $_POST['email'];
    $password = $_POST['password'];

    // 查找匹配的用户记录
    $sql = "SELECT * FROM users WHERE email = '$email' AND password = '$password' AND verified = 1";
    $result = $conn->query($sql);

    if($result->num_rows > 0) {
        // 登录成功
        echo "登录成功！欢迎回来，" . $email;
    } else {
        // 登录失败
        echo "登录失败，请检查邮箱、密码或验证状态。";
    }
}

// 关闭数据库连接
$conn->close();
?>