grocy/middleware/JsonMiddleware.php

<?php

namespace Grocy\Middleware;

class JsonMiddleware extends BaseMiddleware
{
	public function __invoke(\Slim\Http\Request $request, \Slim\Http\Response $response, callable $next)
	{
		$response = $next($request, $response);

		if ($response->hasHeader('Content-Disposition'))
		{
			return $response;
		}
		else
		{
			return $response->withHeader('Content-Type', 'application/json');
		}
	}
}