feature #11324 [SecurityBundle] error helper added symfony/symfony#11147 (i3or1s)

This PR was squashed before being merged into the 2.6-dev branch (closes #11324).

Discussion
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[SecurityBundle] error helper added symfony/symfony#11147

Added helper that extracts last authentication error and username.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | [ #11147 ]
| License       | MIT
| Doc PR        | symfony/symfony-docs#3996

Commits
-------

1722f60 [SecurityBundle] error helper added symfony/symfony#11147

Author: fabpot

Authentication/AuthenticationUtils.php

@@ -0,0 +1,87 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Security\Http\Authentication;
+
+use Symfony\Component\HttpFoundation\RequestStack;
+use Symfony\Component\Security\Core\Exception\AuthenticationException;
+use Symfony\Component\Security\Core\SecurityContextInterface;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Extracts Security Errors from Request
+ *
+ * @author Boris Vujicic <boris.vujicic@gmail.com>
+ */
+class AuthenticationUtils
+{
+    /**
+     * @var RequestStack
+     */
+    private $requestStack;
+
+    /**
+     * @param RequestStack $requestStack
+     */
+    public function __construct(RequestStack $requestStack)
+    {
+        $this->requestStack = $requestStack;
+    }
+
+    /**
+     * @param bool $clearSession
+     * @return null|AuthenticationException
+     */
+    public function getLastAuthenticationError($clearSession = true)
+    {
+        $request = $this->getRequest();
+        $session = $request->getSession();
+        $authenticationException = null;
+
+        if ($request->attributes->has(SecurityContextInterface::AUTHENTICATION_ERROR)) {
+            $authenticationException = $request->attributes->get(SecurityContextInterface::AUTHENTICATION_ERROR);
+        } elseif ($session !== null && $session->has(SecurityContextInterface::AUTHENTICATION_ERROR)) {
+            $authenticationException = $session->get(SecurityContextInterface::AUTHENTICATION_ERROR);
+
+            if ($clearSession) {
+                $session->remove(SecurityContextInterface::AUTHENTICATION_ERROR);
+            }
+
+        }
+
+        return $authenticationException;
+    }
+
+    /**
+     * @return string
+     */
+    public function getLastUsername()
+    {
+        $session = $this->getRequest()->getSession();
+
+        return null === $session ? '' : $session->get(SecurityContextInterface::LAST_USERNAME);
+    }
+
+    /**
+     * @return Request
+     * @throws \LogicException
+     */
+    private function getRequest()
+    {
+        $request = $this->requestStack->getCurrentRequest();
+
+        if (null === $request) {
+            throw new \LogicException('Request should exist so it can be processed for error.');
+        }
+
+        return $request;
+    }
+}