PHPを使ってユーザー登録・ログイン機能を開発する方法

CREATE TABLE users (
   id INT(11) AUTO_INCREMENT PRIMARY KEY,
   username VARCHAR(50) NOT NULL,
   password VARCHAR(255) NOT NULL
);

<?php
if(isset($_POST['submit'])) {
    $username = $_POST['username'];
    $password = $_POST['password'];
    $confirm_password = $_POST['confirm_password'];
    
    // 验证表单输入是否合法
    if(empty($username) || empty($password) || empty($confirm_password)) {
        echo "请填写所有必填字段";
    } elseif($password != $confirm_password) {
        echo "两次输入的密码不一致";
    } else {
        // 密码加密
        $hashed_password = password_hash($password, PASSWORD_DEFAULT);
        
        // 将用户信息插入数据库
        $sql = "INSERT INTO users (username, password) VALUES ('$username', '$hashed_password')";
        if(mysqli_query($conn, $sql)) {
            echo "注册成功";
        } else {
            echo "注册失败，请稍后再试";
        }
    }
}
?>

<form method="post" action="">
    <input type="text" name="username" placeholder="用户名" required>
    <input type="password" name="password" placeholder="密码" required>
    <input type="password" name="confirm_password" placeholder="确认密码" required>
    <input type="submit" name="submit" value="注册">
</form>

<?php
if(isset($_POST['submit'])) {
    $username = $_POST['username'];
    $password = $_POST['password'];
    
    // 查询数据库中是否存在相应的用户名
    $sql = "SELECT * FROM users WHERE username = '$username'";
    $result = mysqli_query($conn, $sql);
    
    if(mysqli_num_rows($result) > 0) {
        $row = mysqli_fetch_assoc($result);
        // 校验密码是否正确
        if(password_verify($password, $row['password'])) {
            echo "登录成功";
        } else {
            echo "密码错误";
        }
    } else {
        echo "用户名不存在";
    }
}
?>

<form method="post" action="">
    <input type="text" name="username" placeholder="用户名" required>
    <input type="password" name="password" placeholder="密码" required>
    <input type="submit" name="submit" value="登录">
</form>