PHP は、知識の質問と回答の Web サイトにユーザーのログイン確認コードとセキュリティ機能を実装します。

<?php
session_start();

$width = 130;
$height = 40;
$length = 4;

$code = '';
$chars = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
$chars_length = strlen($chars);

for ($i = 0; $i < $length; $i++) {
    $code .= $chars[rand(0, $chars_length - 1)];
}

$_SESSION['code'] = $code;

$image = imagecreatetruecolor($width, $height);
$background_color = imagecolorallocate($image, 255, 255, 255);
$text_color = imagecolorallocate($image, 0, 0, 0);

imagefilledrectangle($image, 0, 0, $width, $height, $background_color);
imagettftext($image, 20, 0, 10, 28, $text_color, 'arial.ttf', $code);

header('Content-type: image/png');
imagepng($image);
imagedestroy($image);
?>

<?php
session_start();

$submitted_code = $_POST['code'];
$stored_code = $_SESSION['code'];

if ($submitted_code == $stored_code) {
    // 验证码匹配成功
    // 执行登录操作
} else {
    // 验证码匹配失败
    // 返回错误信息
}
?>

<?php
$password = $_POST['password'];

$hash = password_hash($password, PASSWORD_DEFAULT);

// 将$hash存储到数据库的密码字段中
?>

<?php
$username = $_POST['username'];
$password = $_POST['password'];

$username = mysqli_real_escape_string($conn, $username);
$password = mysqli_real_escape_string($conn, $password);

// 执行SQL查询
?>

<?php
session_start();

$username = $_POST['username'];
$password = $_POST['password'];

// 检查登录尝试次数
if (isset($_SESSION['login_attempts'])) {
    $_SESSION['login_attempts'] += 1;
} else {
    $_SESSION['login_attempts'] = 1;
}

// 检查登录尝试次数是否超过限制
if ($_SESSION['login_attempts'] > 5) {
    // 锁定账号一段时间
    $_SESSION['locked'] = true;
} else {
    // 执行登录操作
}
?>