如何使用PHP编写具有邮箱验证功能的安全登录注册系统？

CREATE TABLE users (
id INT(11) AUTO_INCREMENT PRIMARY KEY,
username VARCHAR(255) NOT NULL,
email VARCHAR(255) NOT NULL,
password VARCHAR(255) NOT NULL,
verified INT(1) NOT NULL DEFAULT 0
);

<?php
// 获取表单输入数据
$username = $_POST['username'];
$email = $_POST['email'];
$password = $_POST['password'];

// 验证用户输入

// 检查用户名是否已被注册

// 检查邮箱格式是否正确

// 生成一个随机验证码字符串
$verificationCode = bin2hex(random_bytes(16));

// 将用户信息保存到数据库
$query = "INSERT INTO users (username, email, password, verification_code) VALUES ('$username', '$email', '$password', '$verificationCode')";
mysqli_query($connection, $query);

// 发送验证邮件
$to = $email;
$subject = '账号激活邮件';
$message = '请点击以下链接激活您的账号：https://example.com/verify.php?code=' . $verificationCode;
$headers = 'From: noreply@example.com' . "
" .
'Reply-To: noreply@example.com' . "
" .
'X-Mailer: PHP/' . phpversion();

mail($to, $subject, $message, $headers);

// 提示用户验证邮件已发送
echo '注册成功！请检查您的邮箱并点击验证链接进行账号激活。';
?>

<?php
$verificationCode = $_GET['code'];

// 在数据库中查找匹配的验证代码
$query = "SELECT * FROM users WHERE verification_code = '$verificationCode' LIMIT 1";
$result = mysqli_query($connection, $query);

// 如果找到匹配的验证代码，更新用户的“verified”字段
if (mysqli_num_rows($result) > 0) {
    $user = mysqli_fetch_assoc($result);
    $userId = $user['id'];

    $updateQuery = "UPDATE users SET verified = 1 WHERE id = '$userId'";
    mysqli_query($connection, $updateQuery);

    echo '邮箱验证成功！您可以登录了。';
} else {
    echo '无效的验证链接。';
}
?>

<?php
$email = $_POST['email'];
$password = $_POST['password'];

// 在数据库中查找匹配的邮箱和密码
$query = "SELECT * FROM users WHERE email = '$email' AND password = '$password' LIMIT 1";
$result = mysqli_query($connection, $query);

// 如果找到匹配的记录，表示登录成功
if (mysqli_num_rows($result) > 0) {
    $user = mysqli_fetch_assoc($result);
    $verified = $user['verified'];

    if ($verified) {
        echo '登录成功！';
    } else {
        echo '账号尚未激活，请检查您的邮箱并点击验证链接进行账号激活。';
    }
} else {
    echo '邮箱或密码输入错误。';
}
?>