diff --git a/core/core.services.yml b/core/core.services.yml
index 0aec7ac..567e757 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -378,12 +378,17 @@ services:
     class: GuzzleHttp\HandlerStack
     public: false
     factory: GuzzleHttp\HandlerStack::create
+    configurator: ['@http_handler_stack_configurator', configure]
+  http_handler_stack_configurator:
+    class: Drupal\Core\Http\HandlerStackConfigurator
+    public: false
+    arguments: ['@service_container']
   http_client:
     class: Drupal\Core\Http\Client
     factory: http_client_factory:fromOptions
   http_client_factory:
     class: Drupal\Core\Http\ClientFactory
-    arguments: ['@handler_stack']
+    arguments: ['@http_handler_stack']
   theme.negotiator:
     class: Drupal\Core\Theme\ThemeNegotiator
     arguments: ['@access_check.theme']
diff --git a/core/lib/Drupal/Core/CoreServiceProvider.php b/core/lib/Drupal/Core/CoreServiceProvider.php
index cac83a6..c9eea1f 100644
--- a/core/lib/Drupal/Core/CoreServiceProvider.php
+++ b/core/lib/Drupal/Core/CoreServiceProvider.php
@@ -10,7 +10,7 @@
 use Drupal\Core\Cache\Context\CacheContextsPass;
 use Drupal\Core\Cache\ListCacheBinsPass;
 use Drupal\Core\DependencyInjection\Compiler\BackendCompilerPass;
-use Drupal\Core\DependencyInjection\Compiler\GuzzleHandlerPass;
+use Drupal\Core\DependencyInjection\Compiler\GuzzleMiddlewarePass;
 use Drupal\Core\DependencyInjection\Compiler\ContextProvidersPass;
 use Drupal\Core\DependencyInjection\Compiler\ProxyServicesPass;
 use Drupal\Core\DependencyInjection\Compiler\RegisterLazyRouteEnhancers;
@@ -76,7 +76,7 @@ public function register(ContainerBuilder $container) {
     // Collect tagged handler services as method calls on consumer services.
     $container->addCompilerPass(new TaggedHandlersPass());
     $container->addCompilerPass(new RegisterStreamWrappersPass());
-    $container->addCompilerPass(new GuzzleHandlerPass());
+    $container->addCompilerPass(new GuzzleMiddlewarePass());
 
     // Add a compiler pass for registering event subscribers.
     $container->addCompilerPass(new RegisterKernelListenersPass(), PassConfig::TYPE_AFTER_REMOVING);
@@ -134,10 +134,10 @@ protected function registerTest(ContainerBuilder $container) {
     if (!drupal_valid_test_ua()) {
       return;
     }
-    // Add the HTTP request subscriber to Guzzle.
+    // Add the HTTP request middleware to Guzzle.
     $container
       ->register('test.http_client.handler', 'Drupal\Core\Test\EventSubscriber\HttpRequestSubscriber')
-      ->addTag('http_client_handler');
+      ->addTag('http_client_middleware');
   }
 
 }
diff --git a/core/lib/Drupal/Core/DependencyInjection/Compiler/GuzzleHandlerPass.php b/core/lib/Drupal/Core/DependencyInjection/Compiler/GuzzleMiddlewarePass.php
similarity index 51%
rename from core/lib/Drupal/Core/DependencyInjection/Compiler/GuzzleHandlerPass.php
rename to core/lib/Drupal/Core/DependencyInjection/Compiler/GuzzleMiddlewarePass.php
index 009e8b2..d2523cf 100644
--- a/core/lib/Drupal/Core/DependencyInjection/Compiler/GuzzleHandlerPass.php
+++ b/core/lib/Drupal/Core/DependencyInjection/Compiler/GuzzleMiddlewarePass.php
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Contains \Drupal\Core\DependencyInjection\Compiler\GuzzleHandlerPass.
+ * Contains \Drupal\Core\DependencyInjection\Compiler\GuzzleMiddlewarePass.
  */
 
 namespace Drupal\Core\DependencyInjection\Compiler;
@@ -11,15 +11,15 @@
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Reference;
 
-class GuzzleHandlerPass implements CompilerPassInterface {
+class GuzzleMiddlewarePass implements CompilerPassInterface {
 
   /**
    * {@inheritdoc}
    */
   public function process(ContainerBuilder $container) {
-    $service_ids = array_keys($container->findTaggedServiceIds('http_client_handler'));
-    $container->getDefinition('http_client')
-      ->addArgument($service_ids);
+    $middleware_ids = array_keys($container->findTaggedServiceIds('http_client_middleware'));
+    $container->getDefinition('http_handler_stack_configurator')
+      ->addArgument($middleware_ids);
   }
 
 }
diff --git a/core/lib/Drupal/Core/Http/ClientFactory.php b/core/lib/Drupal/Core/Http/ClientFactory.php
index 9c2eee2..b9d597a 100644
--- a/core/lib/Drupal/Core/Http/ClientFactory.php
+++ b/core/lib/Drupal/Core/Http/ClientFactory.php
@@ -62,7 +62,7 @@ public function fromOptions(array $config = []) {
     // The entire config array is merged/configurable to allow Guzzle client
     // options outside of 'defaults' to be changed, such as 'adapter', or
     // 'message_factory'.
-    $config = NestedArray::mergeDeep(array($default_config), Settings::get('http_client_config', array()));
+    $config = NestedArray::mergeDeep($config, $default_config, Settings::get('http_client_config', array()));
 
     return new Client($config);
   }
diff --git a/core/lib/Drupal/Core/Http/HandlerStackConfigurator.php b/core/lib/Drupal/Core/Http/HandlerStackConfigurator.php
new file mode 100644
index 0000000..d5aa3c5
--- /dev/null
+++ b/core/lib/Drupal/Core/Http/HandlerStackConfigurator.php
@@ -0,0 +1,62 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Http\HandlerStackConfigurator.
+ */
+
+namespace Drupal\Core\Http;
+
+use GuzzleHttp\HandlerStack;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Defines a class for configuring middlewares on the http handler stack.
+ *
+ * The http_client service requires a handler stack to perform http requests.
+ * This is provided by the http_handler_stack service. Modules wishing to add
+ * additional middlewares to the handler stack can create services and tag them
+ * as http_client_middleware. Each service must contain an __invoke method that
+ * returns a closure which will serve as the middleware.
+ *
+ * @see \Drupal\Core\Http\Client
+ * @see \Drupal\Core\Test\EventSubscriber\HttpRequestSubscriber
+ */
+class HandlerStackConfigurator {
+
+  /**
+   * Array of middlewares to add to the handler stack.
+   *
+   * @var callable[]
+   */
+  protected $middlewares = [];
+
+  /**
+   * Contructs a new HandlerStackConfigurator object.
+   *
+   * @param \Symfony\Component\DependencyInjection\ContainerInterface $container
+   *   The service container.
+   */
+  public function __construct(ContainerInterface $container, array $middleware_ids) {
+    foreach ($middleware_ids as $middleware_id) {
+      $middleware = $container->get($middleware_id);
+      if (method_exists($middleware, '__invoke')) {
+        $class = get_class($middleware);
+        $this->middlewares[$middleware_id] = $class();
+      }
+    }
+  }
+
+  /**
+   * Configures the handler stack using services tagged as http_middleware.
+   *
+   * @param \GuzzleHttp\HandlerStack $handler_stack
+   *   The handler stack
+   */
+  public function configure(HandlerStack $handler_stack) {
+    foreach ($this->middlewares as $middleware_id => $middleware) {
+      $handler_stack->push($middleware, $middleware_id);
+    }
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Http/StackHandlerRegistrationInterface.php b/core/lib/Drupal/Core/Http/StackHandlerRegistrationInterface.php
deleted file mode 100644
index 948bf02..0000000
--- a/core/lib/Drupal/Core/Http/StackHandlerRegistrationInterface.php
+++ /dev/null
@@ -1,20 +0,0 @@
-<?php
-/**
- * @file
- * Contains StackHandlerRegistrationInterface.php
- */
-
-namespace Drupal\Core\Http;
-
-
-interface StackHandlerRegistrationInterface {
-
-  /**
-   * Registers a new callable in the http_client stack handler.
-   *
-   * @return callable
-   *   Returns a callable to be pushed onto the HandlerStack.
-   */
-  public function register();
-
-}
diff --git a/core/lib/Drupal/Core/Test/EventSubscriber/HttpRequestSubscriber.php b/core/lib/Drupal/Core/Test/EventSubscriber/HttpRequestSubscriber.php
index b001638..e3d2504 100644
--- a/core/lib/Drupal/Core/Test/EventSubscriber/HttpRequestSubscriber.php
+++ b/core/lib/Drupal/Core/Test/EventSubscriber/HttpRequestSubscriber.php
@@ -14,12 +14,12 @@
 /**
  * Overrides the User-Agent HTTP header for outbound HTTP requests.
  */
-class HttpRequestSubscriber implements StackHandlerRegistrationInterface {
+class HttpRequestSubscriber {
 
   /**
    * {@inheritdoc}
    */
-  public function register() {
+  public function __invoke() {
     // If the database prefix is being used by SimpleTest to run the tests in a copied
     // database then set the user-agent header to the database prefix so that any
     // calls to other Drupal pages will run the SimpleTest prefixed database. The
diff --git a/core/modules/aggregator/src/Plugin/aggregator/fetcher/DefaultFetcher.php b/core/modules/aggregator/src/Plugin/aggregator/fetcher/DefaultFetcher.php
index b242519..b7a0421 100644
--- a/core/modules/aggregator/src/Plugin/aggregator/fetcher/DefaultFetcher.php
+++ b/core/modules/aggregator/src/Plugin/aggregator/fetcher/DefaultFetcher.php
@@ -89,9 +89,10 @@ public function fetch(FeedInterface $feed) {
 
       /** @var \Psr\Http\Message\UriInterface $actual_uri */
       $actual_uri = NULL;
-      $response = $this->httpClientFactory->fromOptions(['on_redirect' => function(RequestInterface $request, ResponseInterface $response, UriInterface $uri) use (&$actual_uri) {
-        $actual_uri = $uri;
-      }])->send($request);
+      $response = $this->httpClientFactory->fromOptions(['allow_redirects' => [
+        'on_redirect' => function(RequestInterface $request, ResponseInterface $response, UriInterface $uri) use (&$actual_uri) {
+        $actual_uri = (string) $uri;
+      }]])->send($request);
 
       // In case of a 304 Not Modified, there is no new content, so return
       // FALSE.
@@ -109,8 +110,7 @@ public function fetch(FeedInterface $feed) {
       $feed->http_headers = $response->getHeaders();
 
       // Update the feed URL in case of a 301 redirect.
-      $actual_uri = (string) $actual_uri;
-      if ($actual_uri != $feed->getUrl()) {
+      if ($actual_uri && $actual_uri !== $feed->getUrl()) {
         $feed->setUrl($actual_uri);
       }
       return TRUE;
diff --git a/core/modules/locale/locale.batch.inc b/core/modules/locale/locale.batch.inc
index 6f2ad73..f549e51 100644
--- a/core/modules/locale/locale.batch.inc
+++ b/core/modules/locale/locale.batch.inc
@@ -238,14 +238,14 @@ function locale_translation_http_check($uri) {
   $logger = \Drupal::logger('locale');
   try {
     $actual_uri = NULL;
-    $response = \Drupal::httpClientFactory()->fromOptions(['on_redirect' => function(RequestInterface $request, ResponseInterface $response, UriInterface $uri) {
-      $actual_uri = $uri;
-    }])->head($uri);
+    $response = \Drupal::httpClientFactory()->fromOptions(['allow_redirects' => [
+      'on_redirect' => function(RequestInterface $request, ResponseInterface $response, UriInterface $uri) use (&$actual_uri) {
+      $actual_uri = (string) $uri;
+    }]])->head($uri);
     $result = array();
 
-    $actual_uri = (string) $actual_uri;
     // Return the effective URL if it differs from the requested.
-    if ($actual_uri != $uri) {
+    if ($actual_uri && $actual_uri !== $uri) {
       $result['location'] = $actual_uri;
     }