diff --git a/framework/core/src/Foundation/AbstractServer.php b/framework/core/src/Foundation/AbstractServer.php
index 5f6115029..6d5de36a0 100644
--- a/framework/core/src/Foundation/AbstractServer.php
+++ b/framework/core/src/Foundation/AbstractServer.php
@@ -42,6 +42,11 @@ abstract class AbstractServer
      */
     protected $config;
 
+    /**
+     * @var callable[]
+     */
+    protected $registerCallbacks = [];
+
     /**
      * @param null $basePath
      * @param null $publicPath
@@ -128,6 +133,14 @@ abstract class AbstractServer
         $this->config = $config;
     }
 
+    /**
+     * @param callable $callback
+     */
+    public function register(callable $callback)
+    {
+        $this->registerCallbacks[] = $callback;
+    }
+
     /**
      * @return Application
      */
@@ -179,6 +192,11 @@ abstract class AbstractServer
             $app->register('Flarum\Api\ApiServiceProvider');
             $app->register('Flarum\Forum\ForumServiceProvider');
             $app->register('Flarum\Admin\AdminServiceProvider');
+
+            foreach ($this->registerCallbacks as $callback) {
+                $callback($app);
+            }
+
             $app->register('Flarum\Extension\ExtensionServiceProvider');
         }