Add route and action for uploading user avatars.

src/Api/Actions/Users/UploadAvatarAction.php

@@ -0,0 +1,21 @@
+<?php namespace Flarum\Api\Actions\Users;
+
+use Flarum\Api\Actions\BaseAction;
+use Flarum\Core\Commands\UploadAvatarCommand;
+use Illuminate\Http\Request;
+
+class UploadAvatarAction extends BaseAction
+{
+    public function handle(Request $request, $routeParams = [])
+    {
+        $userId = array_get($routeParams, 'id');
+        $file = $request->file('avatar');
+
+        $this->dispatch(
+            new UploadAvatarCommand($userId, $this->actor->getUser(), $file),
+            $routeParams
+        );
+
+        return $this->respondWithoutContent(201);
+    }
+}

src/Api/routes.php

@@ -59,6 +59,11 @@ Route::group(['prefix' => 'api', 'middleware' => 'Flarum\Api\Middleware\LoginWit
         'uses' => $action('Flarum\Api\Actions\Users\DeleteAction')
     ]);
 
+    Route::post('users/{id}/avatar', [
+        'as' => 'flarum.api.users.avatar.upload',
+        'uses' => $action('Flarum\Api\Actions\Users\UploadAvatarAction')
+    ]);
+
     /*
     |--------------------------------------------------------------------------
     | Activity