diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7ee386a..4f31e29 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,14 @@ All Notable changes to `mapudo/guzzle-bundle` will be documented in this file.
 
 Updates should follow the [Keep a CHANGELOG](http://keepachangelog.com/) principles.
 
+## [2.4.0] - 2019-05-22
+### Added
+- Added middleware to automatically append api key query parameters.
+- Added more extensive description for middleware
+### Changed
+- Changed code style of middleware classes to fit with newest standards WITHOUT breaking BC
+- Clean up readme
+
 ## [2.3.0] - 2019-04-12
 ### Added
 - Added functionality to define channels when registering LogMiddleware. This allows a user, to inject a specific logger into the LogMiddleware dependent on the channel.
diff --git a/LICENSE b/LICENSE.md
similarity index 100%
rename from LICENSE
rename to LICENSE.md
diff --git a/README.md b/README.md
index a79992b..3cc06a1 100644
--- a/README.md
+++ b/README.md
@@ -100,12 +100,15 @@ available to configure via the config.
 
 ```php
 <?php
+use GuzzleHttp\TransferStats;
+use Symfony\Component\HttpFoundation\Request;
+
 $client = $container->get('guzzle.client.test_client');
-$moreOptions = ['on_stats' => function (\GuzzleHttp\TransferStats $stats) {
+$moreOptions = ['on_stats' => static function (TransferStats $stats) {
     echo $stats->getEffectiveUri() . "\n";
     echo $stats->getTransferTime() . "\n";
 }];
-$client->requestAsync(\Symfony\Component\HttpFoundation\Request::METHOD_GET, '/path/without/base_uri', $moreOptions);
+$client->requestAsync(Request::METHOD_GET, '/path/without/base_uri', $moreOptions);
 ```
 
 **Note**: *Clear your cache after adding a new log handler or a middleware 
@@ -174,6 +177,10 @@ For example, to write your own handler, take the response and request array out
 
 ```php
 <?php
+use Mapudo\Bundle\GuzzleBundle\Log\Model\Request;
+use Mapudo\Bundle\GuzzleBundle\Log\Model\Response;
+
+/** @noinspection PhpUndefinedVariableInspection */
 if ($record['context']) {
     $response = null;
     if (!empty($record['context']['response'])) {
@@ -190,8 +197,43 @@ if ($record['context']) {
 or just do what you want.
 
 ### Middleware
-This bundle comes with two middleware services already implemented. One 
-to dispatch events and one to log with given handlers.
+This bundle comes with multiple middleware services already implemented.
+
+#### Event dispatch middleware
+The event dispatch middleware fires two events. One before the request is sent and one after the request has been sent (i. e. when we have a response). You can hook into these events by listening for
+
+* `guzzle_event.pre_transaction`
+* `guzzle_event.post_transaction`
+
+#### Log middleware
+The log middleware receives a logger as an argument and will use this logger along with it's definition, i.e. in which channel to log, for which level etc. to log BOTH request and response data including duration times for a request.
+
+### Authentication middleware
+This bundle offers middleware that automatically add authentication data to a request.
+#### Api key
+If you make requests to an API that requires an API key for authentication you can register a service definition for the `Mapudo\Bundle\GuzzleBundle\Middleware\Authentication\ApiKeyMiddleware`
+
+This middleware receives two arguments, while the second one is optional.
+
+* First argument is the api key to use
+* Second argument is the query parameter name  that will be used for the key which defaults to `key`.
+
+So let's say you register your middleware like this
+
+```yaml
+services:
+    guzzle.middleware.authentication.api_key:
+        class: Mapudo\Bundle\GuzzleBundle\Middleware\Authentication\ApiKeyMiddleware
+        arguments:
+            - 'totallySecretString'
+            - 'api_key'
+        tags:
+            - { name: guzzle.middleware, method: authenticate, client: test_client }
+```
+
+and a request to `https://api.google.com/search-results` is made, the Middleware would transform the URI to `https://api.google.com/search-results?api_key=totallySecretString`
+
+You can also add your own authentication middleware by implementing the `AuthenticationMiddlewareInterface`
 
 #### Add your own Middleware
 The bundle supports registering Middlewares by using `__invoke()` or creating a custom
diff --git a/Tests/Middleware/Authentication/ApiKeyMiddlewareTest.php b/Tests/Middleware/Authentication/ApiKeyMiddlewareTest.php
new file mode 100644
index 0000000..17dd4eb
--- /dev/null
+++ b/Tests/Middleware/Authentication/ApiKeyMiddlewareTest.php
@@ -0,0 +1,40 @@
+<?php
+declare(strict_types=1);
+
+namespace Mapudo\Bundle\GuzzleBundle\Tests\Middleware\Authentication;
+
+use GuzzleHttp\Psr7\Request;
+use Mapudo\Bundle\GuzzleBundle\Middleware\Authentication\ApiKeyMiddleware;
+use PHPUnit\Framework\Assert;
+use PHPUnit\Framework\TestCase;
+use Psr\Http\Message\RequestInterface;
+
+class ApiKeyMiddlewareTest extends TestCase
+{
+    /** @var ApiKeyMiddleware */
+    private $apiKeyMiddleware;
+
+    protected function setUp()
+    {
+        $this->apiKeyMiddleware = new ApiKeyMiddleware(
+            'totallySecretApiKey',
+            'api_key'
+        );
+    }
+
+    public function testAuthenticate()
+    {
+        $handler = static function (RequestInterface $request) {
+            Assert::assertSame('api_key=totallySecretApiKey', $request->getUri()->getQuery());
+            Assert::assertSame(
+                'https://api.google.com/calendar?api_key=totallySecretApiKey',
+                (string)$request->getUri()
+            );
+        };
+
+        $request = new Request('GET', 'https://api.google.com/calendar');
+        $options = ['options_are_unimportant_here'];
+
+        $this->apiKeyMiddleware->authenticate()($handler)($request, $options);
+    }
+}
diff --git a/src/Middleware/Authentication/ApiKeyMiddleware.php b/src/Middleware/Authentication/ApiKeyMiddleware.php
new file mode 100644
index 0000000..e53c75c
--- /dev/null
+++ b/src/Middleware/Authentication/ApiKeyMiddleware.php
@@ -0,0 +1,38 @@
+<?php
+declare(strict_types=1);
+
+namespace Mapudo\Bundle\GuzzleBundle\Middleware\Authentication;
+
+use Closure;
+use GuzzleHttp\Psr7\Uri;
+use Psr\Http\Message\RequestInterface;
+
+final class ApiKeyMiddleware implements AuthenticationMiddlewareInterface
+{
+    /** @var string */
+    private $apiKey;
+
+    /** @var string */
+    private $apiKeyParameterName;
+
+    public function __construct(string $apiKey, string $apiKeyParameterName = 'key')
+    {
+        $this->apiKey = $apiKey;
+        $this->apiKeyParameterName = $apiKeyParameterName;
+    }
+
+    public function authenticate(): Closure
+    {
+        return function (callable $handler) {
+            return function (RequestInterface $request, array $options) use ($handler) {
+                $newRequest = $request->withUri(Uri::withQueryValue(
+                    $request->getUri(),
+                    $this->apiKeyParameterName,
+                    $this->apiKey
+                ));
+
+                return $handler($newRequest, $options);
+            };
+        };
+    }
+}
diff --git a/src/Middleware/Authentication/AuthenticationMiddlewareInterface.php b/src/Middleware/Authentication/AuthenticationMiddlewareInterface.php
new file mode 100644
index 0000000..7ac28ef
--- /dev/null
+++ b/src/Middleware/Authentication/AuthenticationMiddlewareInterface.php
@@ -0,0 +1,11 @@
+<?php
+declare(strict_types=1);
+
+namespace Mapudo\Bundle\GuzzleBundle\Middleware\Authentication;
+
+use Closure;
+
+interface AuthenticationMiddlewareInterface
+{
+    public function authenticate(): Closure;
+}
diff --git a/src/Middleware/EventDispatchMiddleware.php b/src/Middleware/EventDispatchMiddleware.php
index 2205461..4ff7985 100644
--- a/src/Middleware/EventDispatchMiddleware.php
+++ b/src/Middleware/EventDispatchMiddleware.php
@@ -26,24 +26,12 @@ class EventDispatchMiddleware
     /** @var string */
     protected $clientName;
 
-    /**
-     * EventDispatchMiddleware constructor.
-     *
-     * @param EventDispatcherInterface $eventDispatcher
-     * @param string                   $clientName
-     */
     public function __construct(EventDispatcherInterface $eventDispatcher, string $clientName)
     {
         $this->eventDispatcher = $eventDispatcher;
         $this->clientName = $clientName;
     }
 
-    /**
-     * Dispatches an event before the transaction is made (i.e. before the response is being gathered)
-     * and another event after the transaction is done (i.e. we now got the response)
-     *
-     * @return Closure
-     */
     public function dispatch(): Closure
     {
         return function (callable $handler) {
diff --git a/src/Middleware/LogMiddleware.php b/src/Middleware/LogMiddleware.php
index a9e1221..fce96c0 100644
--- a/src/Middleware/LogMiddleware.php
+++ b/src/Middleware/LogMiddleware.php
@@ -2,6 +2,7 @@
 
 namespace Mapudo\Bundle\GuzzleBundle\Middleware;
 
+use Closure;
 use GuzzleHttp\Exception\RequestException;
 use GuzzleHttp\MessageFormatter;
 use GuzzleHttp\TransferStats;
@@ -9,6 +10,7 @@
 use Psr\Http\Message\ResponseInterface;
 use Psr\Log\LoggerInterface;
 use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
+use function GuzzleHttp\Promise\rejection_for;
 
 /**
  * Class LogMiddleware
@@ -32,13 +34,6 @@ class LogMiddleware
     /** @var string|null */
     protected $clientName;
 
-    /**
-     * LogMiddleware constructor.
-     *
-     * @param LoggerInterface     $logger
-     * @param MessageFormatter    $formatter
-     * @param NormalizerInterface $normalizer
-     */
     public function __construct(LoggerInterface $logger, MessageFormatter $formatter, NormalizerInterface $normalizer)
     {
         $this->logger = $logger;
@@ -46,11 +41,7 @@ public function __construct(LoggerInterface $logger, MessageFormatter $formatter
         $this->normalizer = $normalizer;
     }
 
-    /**
-     * Log each request
-     * @return \Closure
-     */
-    public function log(): \Closure
+    public function log(): Closure
     {
         $logger    = $this->logger;
         $formatter = $this->formatter;
@@ -58,7 +49,7 @@ public function log(): \Closure
         return function (callable $handler) use ($logger, $formatter) {
             return function (RequestInterface $request, array $options) use ($handler, $logger, $formatter) {
                 $duration = null;
-                $options['on_stats'] = function (TransferStats $stats) use (&$duration) {
+                $options['on_stats'] = static function (TransferStats $stats) use (&$duration) {
                     $duration = $stats->getTransferTime();
                 };
 
@@ -77,19 +68,13 @@ function ($reason) use ($logger, $request, $formatter, &$duration) {
                         $message  = $formatter->format($request, $response, $reason);
                         $logger->error($message, $this->buildContext($request, $response, $duration));
 
-                        return \GuzzleHttp\Promise\rejection_for($reason);
+                        return rejection_for($reason);
                     }
                 );
             };
         };
     }
 
-    /**
-     * Sets the client name. Used to distinguish between clients.
-     *
-     * @param string $clientName
-     * @return LogMiddleware
-     */
     public function setClientName(string $clientName): LogMiddleware
     {
         $this->clientName = $clientName;
@@ -102,6 +87,7 @@ private function buildContext(
         float $duration = null
     ): array {
         $request->getBody()->rewind();
+        /** @noinspection PhpUnhandledExceptionInspection */
         $context = [
             'request' => $this->normalizer->normalize($request),
             'client' => $this->clientName,
@@ -109,6 +95,7 @@ private function buildContext(
         ];
 
         if ($response !== null) {
+            /** @noinspection PhpUnhandledExceptionInspection */
             $context['response'] = $this->normalizer->normalize($response);
         }