PHP と電子メール検証を使用して安全なログインおよび登録システムを実装するにはどうすればよいですか?

<form method="post" action="">
  <input type="text" name="username" placeholder="用户名" required><br>
  <input type="email" name="email" placeholder="邮箱" required><br>
  <input type="password" name="password" placeholder="密码" required><br>
  <input type="submit" name="register" value="注册">
</form>

if (isset($_POST['register'])) {
  $username = $_POST['username'];
  $email = $_POST['email'];
  $password = $_POST['password'];
  $code = md5(uniqid(rand()));

  $insert_query = "INSERT INTO users (username, email, password, code) 
                   VALUES ('$username', '$email', '$password', '$code')";
  mysqli_query($connection, $insert_query);

  $to = $email;
  $subject = "验证您的邮箱";
  $message = "点击以下链接验证您的邮箱：

";
  $message .= "https://example.com/verify.php?email=$email&code=$code";
  $headers = "From: example@example.com";

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

  echo "请检查您的邮箱以完成注册。";
}

<form method="post" action="">
  <input type="email" name="email" placeholder="邮箱" required><br>
  <input type="password" name="password" placeholder="密码" required><br>
  <input type="submit" name="login" value="登录">
</form>

if (isset($_POST['login'])) {
  $email = $_POST['email'];
  $password = $_POST['password'];

  $login_query = "SELECT * FROM users WHERE email='$email' AND password='$password' AND active='1'";
  $result = mysqli_query($connection, $login_query);

  if (mysqli_num_rows($result) == 1) {
    echo "登录成功！";
  } else {
    echo "登录失败，请检查您的邮箱和密码。";
  }
}

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

$update_query = "UPDATE users SET active='1' WHERE email='$email' AND code='$code'";
mysqli_query($connection, $update_query);

echo "您的邮箱已通过验证，现在可以登录了！";
?>