PHP で電子メール認証ログインおよび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
$conn = new mysqli("localhost", "username", "password", "database");
if ($conn->connect_error) {
    die("数据库连接失败：" . $conn->connect_error);
}

$email = $_POST["email"];
$password = $_POST["password"];

// 邮箱是否已被注册
$sql = "SELECT * FROM users WHERE email = '$email'";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
    die("该邮箱已被注册，请直接登录或使用其他邮箱进行注册");
}

// 生成随机验证码
$verificationCode = substr(md5(time()), 0, 6);

// 将验证码存入数据库
$sql = "INSERT INTO verification_codes (email, code) VALUES ('$email', '$verificationCode')";
if ($conn->query($sql) !== TRUE) {
    die("验证码保存失败：" . $conn->error);
}

// 发送验证邮件
$to = $email;
$subject = "邮箱验证邮件";
$message = "您正在注册账号，验证码为：" . $verificationCode;
$headers = "From: [发件人邮箱]";

if (mail($to, $subject, $message, $headers)) {
    echo "验证邮件已发送，请查收并完成注册";
} else {
    echo "邮件发送失败，请稍后再试";
}

$conn->close();

?>

<?php

// 连接数据库
$conn = new mysqli("localhost", "username", "password", "database");
if ($conn->connect_error) {
    die("数据库连接失败：" . $conn->connect_error);
}

$email = $_POST["email"];
$password = $_POST["password"];
$verificationCode = $_POST["verificationCode"];

// 检查邮箱和密码是否匹配
$sql = "SELECT * FROM users WHERE email = '$email' AND password = '$password'";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
    // 验证码是否正确
    $sql = "SELECT * FROM verification_codes WHERE email = '$email' AND code = '$verificationCode'";
    $result = $conn->query($sql);
    if ($result->num_rows > 0) {
        echo "登录成功";
    } else {
        echo "验证码错误";
    }
} else {
    echo "邮箱或密码错误";
}

$conn->close();

?>