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<?php
declare(strict_types=1);
// CSRF token generation and validation.
// Prevents attackers from tricking logged-in users into submitting unwanted requests.
// See README.md for a full explanation of the CSRF attack and how tokens prevent it.
namespace App;
class Csrf
{
public static function generate(): string
{
// Reuse the token for the whole session so multiple tabs/forms work
if (empty($_SESSION['csrf_token'])) {
$_SESSION['csrf_token'] = bin2hex(random_bytes(32));
}
return $_SESSION['csrf_token'];
}
public static function validate(string $token): bool
{
// hash_equals() prevents timing attacks (constant-time comparison)
return isset($_SESSION['csrf_token']) && hash_equals($_SESSION['csrf_token'], $token);
}
public static function field(): string
{
// Returns a hidden <input> to embed in HTML forms
$token = htmlspecialchars(self::generate());
return '<input type="hidden" name="csrf_token" value="' . $token . '">';
}
}
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