diff --git a/.php_cs.dist b/.php_cs.dist
@@ -54,6 +54,11 @@ return PhpCsFixer\Config::create()
         'strict_comparison' => true,
         'strict_param' => true,
         'void_return' => true,
+        // Remove when https://github.com/FriendsOfPHP/PHP-CS-Fixer/pull/3222 has been merged
+        'LeoFeyer/optimize_native_functions' => true,
+    ])
+    ->registerCustomFixers([
+        new LeoFeyer\PhpCsFixer\OptimizeNativeFunctionsFixer()
     ])
     ->setFinder($finder)
     ->setRiskyAllowed(true)

diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Contao core bundle change log
 
+### 4.5.4 (2018-02-14)
+
+ * Preserve custom CSS classes in the back end navigation (see #1357).
+
 ### 4.5.3 (2018-01-23)
 
  * Correctly select folders as gallery source (see #1328).

diff --git a/.github/CONTRIBUTING.md → CONTRIBUTING.md b/.github/CONTRIBUTING.md → CONTRIBUTING.md
@@ -18,8 +18,9 @@ propose changes to this document in a pull request.
 ## Pull requests
 
 * Follow the Contao coding standards.
-* Create your pull request against the `master` branch for bug fixes or the
-  `develop` branch for new features.
+* For new features, create your pull request against the `master` branch.
+* For bug fixes, create your pull request against the lowest affected branch,
+  e.g. `4.4` if the bug is in Contao 4.4 or `4.5` if the bug is in Contao 4.5.
 * Include screenshots in your pull request whenever possible.
 
 ## Git commit messages
@@ -29,4 +30,4 @@ propose changes to this document in a pull request.
 * Reference issues and pull requests liberally.
 
 [1]: https://github.com/contao
-[2]: https://demo.contao.org
+[2]: https://demo.contao.org/contao
diff --git a/LICENSE.md b/LICENSE.md
@@ -0,0 +1,165 @@
+                   GNU LESSER GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+
+  This version of the GNU Lesser General Public License incorporates
+the terms and conditions of version 3 of the GNU General Public
+License, supplemented by the additional permissions listed below.
+
+  0. Additional Definitions.
+
+  As used herein, "this License" refers to version 3 of the GNU Lesser
+General Public License, and the "GNU GPL" refers to version 3 of the GNU
+General Public License.
+
+  "The Library" refers to a covered work governed by this License,
+other than an Application or a Combined Work as defined below.
+
+  An "Application" is any work that makes use of an interface provided
+by the Library, but which is not otherwise based on the Library.
+Defining a subclass of a class defined by the Library is deemed a mode
+of using an interface provided by the Library.
+
+  A "Combined Work" is a work produced by combining or linking an
+Application with the Library.  The particular version of the Library
+with which the Combined Work was made is also called the "Linked
+Version".
+
+  The "Minimal Corresponding Source" for a Combined Work means the
+Corresponding Source for the Combined Work, excluding any source code
+for portions of the Combined Work that, considered in isolation, are
+based on the Application, and not on the Linked Version.
+
+  The "Corresponding Application Code" for a Combined Work means the
+object code and/or source code for the Application, including any data
+and utility programs needed for reproducing the Combined Work from the
+Application, but excluding the System Libraries of the Combined Work.
+
+  1. Exception to Section 3 of the GNU GPL.
+
+  You may convey a covered work under sections 3 and 4 of this License
+without being bound by section 3 of the GNU GPL.
+
+  2. Conveying Modified Versions.
+
+  If you modify a copy of the Library, and, in your modifications, a
+facility refers to a function or data to be supplied by an Application
+that uses the facility (other than as an argument passed when the
+facility is invoked), then you may convey a copy of the modified
+version:
+
+   a) under this License, provided that you make a good faith effort to
+   ensure that, in the event an Application does not supply the
+   function or data, the facility still operates, and performs
+   whatever part of its purpose remains meaningful, or
+
+   b) under the GNU GPL, with none of the additional permissions of
+   this License applicable to that copy.
+
+  3. Object Code Incorporating Material from Library Header Files.
+
+  The object code form of an Application may incorporate material from
+a header file that is part of the Library.  You may convey such object
+code under terms of your choice, provided that, if the incorporated
+material is not limited to numerical parameters, data structure
+layouts and accessors, or small macros, inline functions and templates
+(ten or fewer lines in length), you do both of the following:
+
+   a) Give prominent notice with each copy of the object code that the
+   Library is used in it and that the Library and its use are
+   covered by this License.
+
+   b) Accompany the object code with a copy of the GNU GPL and this license
+   document.
+
+  4. Combined Works.
+
+  You may convey a Combined Work under terms of your choice that,
+taken together, effectively do not restrict modification of the
+portions of the Library contained in the Combined Work and reverse
+engineering for debugging such modifications, if you also do each of
+the following:
+
+   a) Give prominent notice with each copy of the Combined Work that
+   the Library is used in it and that the Library and its use are
+   covered by this License.
+
+   b) Accompany the Combined Work with a copy of the GNU GPL and this license
+   document.
+
+   c) For a Combined Work that displays copyright notices during
+   execution, include the copyright notice for the Library among
+   these notices, as well as a reference directing the user to the
+   copies of the GNU GPL and this license document.
+
+   d) Do one of the following:
+
+       0) Convey the Minimal Corresponding Source under the terms of this
+       License, and the Corresponding Application Code in a form
+       suitable for, and under terms that permit, the user to
+       recombine or relink the Application with a modified version of
+       the Linked Version to produce a modified Combined Work, in the
+       manner specified by section 6 of the GNU GPL for conveying
+       Corresponding Source.
+
+       1) Use a suitable shared library mechanism for linking with the
+       Library.  A suitable mechanism is one that (a) uses at run time
+       a copy of the Library already present on the user's computer
+       system, and (b) will operate properly with a modified version
+       of the Library that is interface-compatible with the Linked
+       Version.
+
+   e) Provide Installation Information, but only if you would otherwise
+   be required to provide such information under section 6 of the
+   GNU GPL, and only to the extent that such information is
+   necessary to install and execute a modified version of the
+   Combined Work produced by recombining or relinking the
+   Application with a modified version of the Linked Version. (If
+   you use option 4d0, the Installation Information must accompany
+   the Minimal Corresponding Source and Corresponding Application
+   Code. If you use option 4d1, you must provide the Installation
+   Information in the manner specified by section 6 of the GNU GPL
+   for conveying Corresponding Source.)
+
+  5. Combined Libraries.
+
+  You may place library facilities that are a work based on the
+Library side by side in a single library together with other library
+facilities that are not Applications and are not covered by this
+License, and convey such a combined library under terms of your
+choice, if you do both of the following:
+
+   a) Accompany the combined library with a copy of the same work based
+   on the Library, uncombined with any other library facilities,
+   conveyed under the terms of this License.
+
+   b) Give prominent notice with the combined library that part of it
+   is a work based on the Library, and explaining where to find the
+   accompanying uncombined form of the same work.
+
+  6. Revised Versions of the GNU Lesser General Public License.
+
+  The Free Software Foundation may publish revised and/or new versions
+of the GNU Lesser General Public License from time to time. Such new
+versions will be similar in spirit to the present version, but may
+differ in detail to address new problems or concerns.
+
+  Each version is given a distinguishing version number. If the
+Library as you received it specifies that a certain numbered version
+of the GNU Lesser General Public License "or any later version"
+applies to it, you have the option of following the terms and
+conditions either of that published version or of any later version
+published by the Free Software Foundation. If the Library as you
+received it does not specify a version number of the GNU Lesser
+General Public License, you may choose any version of the GNU Lesser
+General Public License ever published by the Free Software Foundation.
+
+  If the Library as you received it specifies that a proxy can decide
+whether future versions of the GNU Lesser General Public License shall
+apply, that proxy's public statement of acceptance of any version is
+permanent authorization for you to choose that version for the
+Library.
diff --git a/README.md b/README.md
@@ -23,7 +23,9 @@ Edit your `composer.json` file and add the following:
 
 ```json
 "require": {
-    "contao/core-bundle": "^4.5"
+    "contao/core-bundle": "4.5.*",
+    "contao/installation-bundle": "^4.5",
+    "php-http/guzzle6-adapter": "^1.1"
 },
 "config": {
     "component-dir": "assets"
@@ -40,6 +42,8 @@ Edit your `composer.json` file and add the following:
 
 Then run `php composer.phar update` to install the vendor files.
 
+Note that you can exchange the `php-http/guzzle6-adapter` package with any other [HTTP client implementation][4]. If you already have an HTTP client implementation, you can omit the package entirely.
+
 
 Activation
 ----------
@@ -65,8 +69,8 @@ class AppKernel extends Kernel
             new Knp\Bundle\MenuBundle\KnpMenuBundle(),
             new Knp\Bundle\TimeBundle\KnpTimeBundle(),
             new Nelmio\CorsBundle\NelmioCorsBundle(),
-            new Nelmio\SecurityBundle\NelmioSecurityBundle(),
             new Contao\CoreBundle\ContaoCoreBundle(),
+            new Contao\InstallationBundle\ContaoInstallationBundle(),
         ];
     }
 
@@ -90,6 +94,9 @@ Configuration
 Add the Contao routes to your `app/config/routing.yml` file:
 
 ```yml
+ContaoInstallationBundle:
+    resource: "@ContaoInstallationBundle/Resources/config/routing.yml"
+
 ContaoCoreBundle:
     resource: "@ContaoCoreBundle/Resources/config/routing.yml"
 ```
@@ -224,10 +231,11 @@ Contao is licensed under the terms of the LGPLv3.
 Getting support
 ---------------
 
-Visit the [support page][4] to learn about the available support options.
+Visit the [support page][5] to learn about the available support options.
 
 
 [1]: https://contao.org
 [2]: https://symfony.com
 [3]: https://github.com/contao/managed-edition
-[4]: https://contao.org/en/support.html
+[4]: https://packagist.org/providers/php-http/client-implementation
+[5]: https://contao.org/en/support.html
diff --git a/composer.json b/composer.json
@@ -53,7 +53,7 @@
         "oyejorge/less.php": "^1.7",
         "patchwork/utf8": "^1.2",
         "phpspec/php-diff": "^1.0",
-        "phpunit/php-token-stream": "^1.4",
+        "phpunit/php-token-stream": "^1.4|^2.0|^3.0",
         "psr/log": "^1.0",
         "sensio/framework-extra-bundle": "^5.0",
         "simplepie/simplepie": "^1.3",
@@ -79,6 +79,7 @@
         "contao/manager-plugin": "<2.0 || >=3.0",
         "doctrine/doctrine-migrations-bundle": "<1.1",
         "doctrine/orm": "<2.4",
+        "lexik/maintenance-bundle": "2.1.4",
         "symfony/swiftmailer-bundle": "2.6.* <2.6.2"
     },
     "require-dev": {
@@ -89,6 +90,7 @@
         "doctrine/doctrine-migrations-bundle": "^1.1",
         "doctrine/orm": "^2.5",
         "friendsofphp/php-cs-fixer": "^2.6",
+        "leofeyer/optimize-native-functions-fixer": "^1.0",
         "lexik/maintenance-bundle": "^2.0",
         "monolog/monolog": "^1.22",
         "php-http/guzzle6-adapter": "^1.1",

diff --git a/src/Csrf/MemoryTokenStorage.php b/src/Csrf/MemoryTokenStorage.php
@@ -92,6 +92,10 @@ public function initialize(array $tokens): void
      */
     public function getUsedTokens(): array
     {
+        if (null === $this->tokens) {
+            return [];
+        }
+
         return array_intersect_key($this->tokens, $this->usedTokens);
     }
 

diff --git a/src/EventListener/AddToSearchIndexListener.php b/src/EventListener/AddToSearchIndexListener.php
@@ -13,7 +13,6 @@
 namespace Contao\CoreBundle\EventListener;
 
 use Contao\CoreBundle\Framework\ContaoFrameworkInterface;
-use Contao\CoreBundle\Routing\ScopeMatcher;
 use Contao\Frontend;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpKernel\Event\PostResponseEvent;
@@ -25,25 +24,18 @@ class AddToSearchIndexListener
      */
     private $framework;
 
-    /**
-     * @var ScopeMatcher
-     */
-    private $scopeMatcher;
-
     /**
      * @var string
      */
     private $fragmentPath;
 
     /**
      * @param ContaoFrameworkInterface $framework
-     * @param ScopeMatcher             $scopeMatcher
      * @param string                   $fragmentPath
      */
-    public function __construct(ContaoFrameworkInterface $framework, ScopeMatcher $scopeMatcher, string $fragmentPath = '_fragment')
+    public function __construct(ContaoFrameworkInterface $framework, string $fragmentPath = '_fragment')
     {
         $this->framework = $framework;
-        $this->scopeMatcher = $scopeMatcher;
         $this->fragmentPath = $fragmentPath;
     }
 
@@ -54,7 +46,7 @@ public function __construct(ContaoFrameworkInterface $framework, ScopeMatcher $s
      */
     public function onKernelTerminate(PostResponseEvent $event): void
     {
-        if (!$this->framework->isInitialized() || !$this->scopeMatcher->isFrontendMasterRequest($event)) {
+        if (!$this->framework->isInitialized()) {
             return;
         }
 

diff --git a/src/EventListener/BackendMenuListener.php b/src/EventListener/BackendMenuListener.php
@@ -64,7 +64,6 @@ public function onBuild(MenuEvent $event): void
             foreach ($categoryData['modules'] as $moduleName => $moduleData) {
                 $moduleNode = $this->createNode($factory, $moduleName, $moduleData);
                 $moduleNode->setCurrent((bool) $moduleData['isActive']);
-                $moduleNode->setAttribute('class', $moduleName);
 
                 $categoryNode->addChild($moduleNode);
             }
@@ -82,13 +81,22 @@ public function onBuild(MenuEvent $event): void
      */
     private function createNode(FactoryInterface $factory, string $name, array $attributes): ItemInterface
     {
+        $classes = [];
+
+        // Remove the default CSS classes and keep potentially existing custom ones (see #1357)
+        if (isset($attributes['class'])) {
+            $classes = array_flip(array_filter(explode(' ', $attributes['class'])));
+            unset($classes['node-expanded'], $classes['node-collapsed'], $classes['trail']);
+        }
+
         return $factory->createItem(
             $name,
             [
                 'label' => $attributes['label'],
                 'attributes' => [
                     'title' => $attributes['title'],
                     'href' => $attributes['href'],
+                    'class' => implode(' ', array_keys($classes)),
                 ],
             ]
         );

diff --git a/src/Picker/PagePickerProvider.php b/src/Picker/PagePickerProvider.php
@@ -72,7 +72,11 @@ public function getDcaAttributes(PickerConfig $config): array
             }
 
             if ($value) {
-                $attributes['value'] = array_map('\intval', explode(',', $value));
+                $intval = function ($val) {
+                    return (int) $val;
+                };
+
+                $attributes['value'] = array_map($intval, explode(',', $value));
             }
 
             return $attributes;

diff --git a/src/Resources/config/listener.yml b/src/Resources/config/listener.yml
@@ -12,7 +12,6 @@ services:
         class: Contao\CoreBundle\EventListener\AddToSearchIndexListener
         arguments:
             - "@contao.framework"
-            - "@contao.routing.scope_matcher"
             - "%fragment.path%"
         tags:
             - { name: kernel.event_listener, event: kernel.terminate, method: onKernelTerminate }