如何使用PHP和郵箱驗證實現安全的登入註冊系統？

<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！";
?>