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Guard.php
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Guard.php
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<?php
namespace Slim\Csrf;
use ArrayAccess;
use Countable;
use Traversable;
use IteratorAggregate;
use RuntimeException;
use Psr\Http\Message\ServerRequestInterface;
use Psr\Http\Message\ResponseInterface;
/**
* CSRF protection middleware.
*/
class Guard
{
/**
* Prefix for CSRF parameters (omit trailing "_" underscore)
*
* @var string
*/
protected $prefix;
/**
* CSRF storage
*
* Should be either an array or an object. If an object is used, then it must
* implement ArrayAccess and should implement Countable and Iterator (or
* IteratorAggregate) if storage limit enforcement is required.
*
* @var array|ArrayAccess
*/
protected $storage;
/**
* Number of elements to store in the storage array
*
* Default is 200, set via constructor
*
* @var integer
*/
protected $storageLimit;
/**
* CSRF Strength
*
* @var int
*/
protected $strength;
/**
* Callable to be executed if the CSRF validation fails
*
* Signature of callable is:
* function($request, $response, $next)
* and a $response must be returned.
*
* @var callable
*/
protected $failureCallable;
/**
* Determines whether or not we should persist the token throughout the duration of the user's session.
*
* For security, Slim-Csrf will *always* reset the token if there is a validation error.
* @var bool True to use the same token throughout the session (unless there is a validation error),
* false to get a new token with each request.
*/
protected $persistentTokenMode;
/**
* Stores the latest key-pair generated by the class
*
* @var array
*/
protected $keyPair;
/**
* Create new CSRF guard
*
* @param string $prefix
* @param null|array|ArrayAccess $storage
* @param null|callable $failureCallable
* @param integer $storageLimit
* @param integer $strength
* @param boolean $persistentTokenMode
* @throws RuntimeException if the session cannot be found
*/
public function __construct(
$prefix = 'csrf',
&$storage = null,
callable $failureCallable = null,
$storageLimit = 200,
$strength = 16,
$persistentTokenMode = false
) {
$this->prefix = rtrim($prefix, '_');
if ($strength < 16) {
throw new RuntimeException('CSRF middleware failed. Minimum strength is 16.');
}
$this->strength = $strength;
$this->storage = &$storage;
$this->setFailureCallable($failureCallable);
$this->setStorageLimit($storageLimit);
$this->setPersistentTokenMode($persistentTokenMode);
$this->keyPair = null;
}
/**
* Retrieve token name key
*
* @return string
*/
public function getTokenNameKey()
{
return $this->prefix . '_name';
}
/**
* Retrieve token value key
*
* @return string
*/
public function getTokenValueKey()
{
return $this->prefix . '_value';
}
/**
* Invoke middleware
*
* @param ServerRequestInterface $request PSR7 request object
* @param ResponseInterface $response PSR7 response object
* @param callable $next Next middleware callable
*
* @return ResponseInterface PSR7 response object
*/
public function __invoke(ServerRequestInterface $request, ResponseInterface $response, callable $next)
{
$this->validateStorage();
// Validate POST, PUT, DELETE, PATCH requests
if (in_array($request->getMethod(), ['POST', 'PUT', 'DELETE', 'PATCH'])) {
$body = $request->getParsedBody();
$body = $body ? (array)$body : [];
$name = isset($body[$this->prefix . '_name']) ? $body[$this->prefix . '_name'] : false;
$value = isset($body[$this->prefix . '_value']) ? $body[$this->prefix . '_value'] : false;
if (!$name || !$value || !$this->validateToken($name, $value)) {
// Need to regenerate a new token, as the validateToken removed the current one.
$request = $this->generateNewToken($request);
$failureCallable = $this->getFailureCallable();
return $failureCallable($request, $response, $next);
}
}
// Generate new CSRF token if persistentTokenMode is false, or if a valid keyPair has not yet been stored
if (!$this->persistentTokenMode || !$this->loadLastKeyPair()) {
$request = $this->generateNewToken($request);
} elseif ($this->persistentTokenMode) {
$pair = $this->loadLastKeyPair() ? $this->keyPair : $this->generateToken();
$request = $this->attachRequestAttributes($request, $pair);
}
// Enforce the storage limit
$this->enforceStorageLimit();
return $next($request, $response);
}
/**
* @param $prefix
* @param $storage
* @return mixed
*/
public function validateStorage()
{
if (is_array($this->storage)) {
return $this->storage;
}
if ($this->storage instanceof ArrayAccess) {
return $this->storage;
}
if (!isset($_SESSION)) {
throw new RuntimeException('CSRF middleware failed. Session not found.');
}
if (!array_key_exists($this->prefix, $_SESSION)) {
$_SESSION[$this->prefix] = [];
}
$this->storage = &$_SESSION[$this->prefix];
return $this->storage;
}
/**
* Generates a new CSRF token
*
* @return array
*/
public function generateToken()
{
// Generate new CSRF token
$name = uniqid($this->prefix);
$value = $this->createToken();
$this->saveToStorage($name, $value);
$this->keyPair = [
$this->prefix . '_name' => $name,
$this->prefix . '_value' => $value
];
return $this->keyPair;
}
/**
* Generates a new CSRF token and attaches it to the Request Object
*
* @param ServerRequestInterface $request PSR7 response object.
*
* @return ServerRequestInterface PSR7 response object.
*/
public function generateNewToken(ServerRequestInterface $request)
{
$pair = $this->generateToken();
$request = $this->attachRequestAttributes($request, $pair);
return $request;
}
/**
* Validate CSRF token from current request
* against token value stored in $_SESSION
*
* @param string $name CSRF name
* @param string $value CSRF token value
*
* @return bool
*/
public function validateToken($name, $value)
{
$token = $this->getFromStorage($name);
if (function_exists('hash_equals')) {
$result = ($token !== false && hash_equals($token, $value));
} else {
$result = ($token !== false && $token === $value);
}
// If we're not in persistent token mode, delete the token.
if (!$this->persistentTokenMode) {
$this->removeFromStorage($name);
}
return $result;
}
/**
* Create CSRF token value
*
* @return string
*/
protected function createToken()
{
return bin2hex(random_bytes($this->strength));
}
/**
* Save token to storage
*
* @param string $name CSRF token name
* @param string $value CSRF token value
*/
protected function saveToStorage($name, $value)
{
$this->storage[$name] = $value;
}
/**
* Get token from storage
*
* @param string $name CSRF token name
*
* @return string|bool CSRF token value or `false` if not present
*/
protected function getFromStorage($name)
{
return isset($this->storage[$name]) ? $this->storage[$name] : false;
}
/**
* Get the most recent key pair from storage.
*
* @return string[]|null Array containing name and value if found, null otherwise
*/
protected function getLastKeyPair()
{
// Use count, since empty ArrayAccess objects can still return false for `empty`
if (count($this->storage) < 1) {
return null;
}
foreach ($this->storage as $name => $value) {
continue;
}
$keyPair = [
$this->prefix . '_name' => $name,
$this->prefix . '_value' => $value
];
return $keyPair;
}
/**
* Load the most recent key pair in storage.
*
* @return bool `true` if there was a key pair to load in storage, false otherwise.
*/
protected function loadLastKeyPair()
{
$this->keyPair = $this->getLastKeyPair();
if ($this->keyPair) {
return true;
}
return false;
}
/**
* Remove token from storage
*
* @param string $name CSRF token name
*/
protected function removeFromStorage($name)
{
$this->storage[$name] = ' ';
unset($this->storage[$name]);
}
/**
* Remove the oldest tokens from the storage array so that there
* are never more than storageLimit tokens in the array.
*
* This is required as a token is generated every request and so
* most will never be used.
*/
protected function enforceStorageLimit()
{
if ($this->storageLimit < 1) {
return;
}
// $storage must be an array or implement Countable and Traversable
if (!is_array($this->storage)
&& !($this->storage instanceof Countable && $this->storage instanceof Traversable)
) {
return;
}
if (is_array($this->storage)) {
while (count($this->storage) > $this->storageLimit) {
array_shift($this->storage);
}
} else {
// array_shift() doesn't work for ArrayAccess, so we need an iterator in order to use rewind()
// and key(), so that we can then unset
$iterator = $this->storage;
if ($this->storage instanceof \IteratorAggregate) {
$iterator = $this->storage->getIterator();
}
while (count($this->storage) > $this->storageLimit) {
$iterator->rewind();
unset($this->storage[$iterator->key()]);
}
}
}
/**
* @param ServerRequestInterface $request
* @param $pair
* @return static
*/
protected function attachRequestAttributes(ServerRequestInterface $request, $pair)
{
return $request->withAttribute($this->prefix . '_name', $pair[$this->prefix . '_name'])
->withAttribute($this->prefix . '_value', $pair[$this->prefix . '_value']);
}
/**
* Getter for failureCallable
*
* @return callable|\Closure
*/
public function getFailureCallable()
{
if (is_null($this->failureCallable)) {
$this->failureCallable = function (ServerRequestInterface $request, ResponseInterface $response, $next) {
$body = new \Slim\Http\Body(fopen('php://temp', 'r+'));
$body->write('Failed CSRF check!');
return $response->withStatus(400)->withHeader('Content-type', 'text/plain')->withBody($body);
};
}
return $this->failureCallable;
}
/**
* Setter for failureCallable
*
* @param mixed $failureCallable Value to set
* @return $this
*/
public function setFailureCallable($failureCallable)
{
$this->failureCallable = $failureCallable;
return $this;
}
/**
* Setter for persistentTokenMode
*
* @param bool $persistentTokenMode True to use the same token throughout the session (unless there is a validation error),
* false to get a new token with each request.
* @return $this
*/
public function setPersistentTokenMode($persistentTokenMode)
{
$this->persistentTokenMode = $persistentTokenMode;
return $this;
}
/**
* Setter for storageLimit
*
* @param integer $storageLimit Value to set
* @return $this
*/
public function setStorageLimit($storageLimit)
{
$this->storageLimit = (int)$storageLimit;
return $this;
}
/**
* Getter for persistentTokenMode
*
* @return bool
*/
public function getPersistentTokenMode()
{
return $this->persistentTokenMode;
}
/**
* @return string
*/
public function getTokenName()
{
return isset($this->keyPair[$this->getTokenNameKey()]) ? $this->keyPair[$this->getTokenNameKey()] : null;
}
/**
* @return string
*/
public function getTokenValue()
{
return isset($this->keyPair[$this->getTokenValueKey()]) ? $this->keyPair[$this->getTokenValueKey()] : null;
}
}