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<?php
class CSRF
{
/** @var string */
const HMAC_ALGORITHM = 'sha256';
/** @var string */
const SESSION_KEY_NAME = '_csrf_key';
/**
* Ensure that a CSRF token is valid for a given action.
*
* @param string $token
* @param string $action
* @return bool
*/
public static function verify($token = '', $action = null)
{
if (!is_string($token) || !is_string($action)) {
return false;
}
$known = self::generate($action);
return hash_equals($known, $token);
}
/**
* Generate a CSRF token for a given action.
*
* @param string $action
* @throws InvalidArgumentException
* @return string
*/
public static function generate($action = null)
{
if (!is_string($action)) {
throw new InvalidArgumentException('A valid action must be defined.');
}
return hash_hmac(self::HMAC_ALGORITHM, $action, self::getKey());
}
/**
* Get HMAC key.
*
* @return string
*/
public static function getKey()
{
if (empty($_SESSION[self::SESSION_KEY_NAME])) {
$_SESSION[self::SESSION_KEY_NAME] = bin2hex(random_bytes(16));
}
return $_SESSION[self::SESSION_KEY_NAME];
}
}
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