如何利用PHP开发一个简单的账号密码生成器

<form action="generate.php" method="post">
    <label for="account_length">账号长度：</label>
    <input type="number" name="account_length" id="account_length" required>
    <br>
    <label for="password_length">密码长度：</label>
    <input type="number" name="password_length" id="password_length" required>
    <br>
    <input type="submit" value="生成">
</form>

<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $account_length = $_POST["account_length"];
    $password_length = $_POST["password_length"];

    $characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $account = '';
    $password = '';

    // 生成随机账号
    for ($i = 0; $i < $account_length; $i++) {
        $account .= $characters[rand(0, strlen($characters) - 1)];
    }

    // 生成随机密码
    for ($i = 0; $i < $password_length; $i++) {
        $password .= $characters[rand(0, strlen($characters) - 1)];
    }

    // 保存账号密码
    $data = "账号：" . $account . "，密码：" . $password . PHP_EOL;
    file_put_contents("accounts.txt", $data, FILE_APPEND);

    echo "生成成功！";
}
?>