Add ResponseMiddleware

app/Middlewares/ResponseMiddleware.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace app\Middlewares;
+
+use Psr\Http\Message\ServerRequestInterface as Request;
+use Psr\Http\Server\RequestHandlerInterface as RequestHandler;
+
+class ResponseMiddleware
+{
+    public function __invoke(Request $request, RequestHandler $handler)
+    {
+        $response = $handler->handle($request);
+        return $response->withHeader('Content-Type', 'application/json');
+    }
+}

index.php

@@ -11,6 +11,7 @@ use app\Controllers\SupervisorController;
 use Slim\Factory\AppFactory;
 use Slim\Routing\RouteCollectorProxy;
 use app\Controllers\WebhookController;
+use app\Middlewares\ResponseMiddleware;
 use Tuupola\Middleware\CorsMiddleware;
 
 include __DIR__ . '/includes/config.php';
@@ -25,6 +26,8 @@ $app->get('/info', function ($request, $response, array $args) {
     ));
     return $response;
 });
+$app->add(new ResponseMiddleware);
+
 $app->add(new CorsMiddleware());
 // Add error middleware
 $app->addErrorMiddleware(true, true, true);