Added new cookbook page to security index.

Author: Kevin Weber

cookbook/security/index.rst

@@ -22,3 +22,4 @@ Security
     csrf_in_login_form
     access_control
     multiple_user_providers
+    throttle_failed_login

cookbook/security/throttle_failed_login.rst

@@ -0,0 +1,117 @@
+.. index::
+    single: Security; Throttle Failed Login
+
+How to Throttle Failed Login Attempts
+=====================================
+
+Sometimes, it's useful to throttle login attempts when you encounter multiple
+recent failed logins.  This can be useful in combatting brute-force
+password-guessing login attacks.  This can be done by implementing a
+``security.authentication.failure`` listener to log failed login attempts, and
+a security provider decorator to deny login attempts from the same IP address.
+
+Authentication Failure Listener
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The purpose of this authentication failure listener is to persist the ip address
+and any other data of the client.  The example here uses a doctrine table to
+persist the data, but you could use another method (Redis, for example).
+
+.. code-block:: php
+
+    namespace AppBundle\Security\Authentication\Listener;
+
+    use Doctrine\ORM\EntityRepositoryInterface;
+    use Symfony\Component\HttpFoundation\RequestStack;
+    use Symfony\Component\Security\Core\Event\AuthenticationFailureEvent;
+
+    class LogFailedLoginAttempt
+    {
+        /**
+         * The doctrine repository to which the failed login attempt will be
+         * persisted.
+         *
+         * @var EntityRepositoryInterface
+         */
+        private $repository;
+
+        /**
+         * The current request contains the ip address and other $_SERVER globals
+         * to persist.
+         *
+         * @var RequestStack
+         */
+        private $requestStack;
+
+        public function __construct(RequestStack $requestStack, EntityRepositoryInterface $repository)
+        {
+            $this->repository = $repository;
+            $this->requestStack = $requestStack;
+        }
+
+        public function onAuthenticationFailureEvent(AuthenticationFailureEvent $event)
+        {
+            $this->repository->logAuthenicationFailure(
+                $event->getToken(),
+                $this->requestStack->getCurrentRequest()
+            );
+        }
+    }
+
+Now you are logging all the relevant details about every failed login attempt.
+
+Security Provider Decorator
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This security provider will decorate another security provider and will reject
+any authentication attempts it needs to throttle.
+
+.. code-block:: php
+
+    namespace AppBundle\Security\Authentication\Provider;
+
+    use Symfony\Component\Security\Core\Exception\AuthenticationException;
+    use Symfony\Component\Security\Core\Authentication\Provider\AuthenticationProviderInterface;
+    use Symfony\Component\Security\Core\Authentication\Token\TokenInterface;
+
+    class LoginThrottleProvider implements AuthenticationProviderInterface
+    {
+        /**
+         * @var AuthenticationProviderInterface
+         */
+        private $decoratedProvider;
+
+        /**
+         * The throttle service decides whether to throttle a certain
+         * ip address or not.
+         */
+        private $throttleService;
+
+        public function __construct(AuthenticationProviderInterface $provider, $throttleService)
+        {
+            $this->decoratedProvider = $provider;
+            $this->throttleService = $throttleService;
+        }
+
+        public function authenticate(TokenInterface $token)
+        {
+            if ($this->throttleService->isThrottled($token)) {
+                throw new AuthenticationException(
+                    'Too many failed authentication attempts.'
+                );
+            }
+
+            return $this->decoratedProvider->authenticate($token);
+        }
+
+        public function supports(TokenInterface $token)
+        {
+            return $this->decoratedProvider->supports($token);
+        }
+    }
+
+The implementation of the throttle service is outside the scope of this
+documentation and will depend on your application's needs.  It is common
+for an application to require additional means of authentication when
+multiple failed logins are detected, such as the addition of a CAPTCHA
+to the login page, or requiring two-factor authentication.