Passing variables between Middlewares using zend-mvc

I'm trying to decipher how to properly blend variables between ZF3 Middleware under the latest release of zend-mvc.

Imagine a route like this:

'sandwich-test' => [ 'type' => \Zend\Router\Http\Literal::class, 'options' => [ 'route' => '/events/sandwich', 'defaults' => [ 'middleware' => [ \Foo\Middleware\JsonWrappingMiddleware::class, \Foo\Middleware\TestMiddleware::class, ], ], ], ], 

In my simple test, I'd like for JsonWrappingMiddleware to simply return in a JsonResponse, the variables returned by TestMiddleware.

Individually, this works:

use Interop\Http\ServerMiddleware\DelegateInterface; use Interop\Http\ServerMiddleware\MiddlewareInterface; use Psr\Http\Message\ServerRequestInterface; use Zend\Diactoros\Response\JsonResponse; class JsonWrappingMiddleware implements MiddlewareInterface { public function process(ServerRequestInterface $request, DelegateInterface $delegate) { return new JsonResponse(['c' => 'd']); } } 

...and...

use Interop\Http\ServerMiddleware\DelegateInterface; use Interop\Http\ServerMiddleware\MiddlewareInterface; use Psr\Http\Message\ServerRequestInterface; use Zend\Diactoros\Response\JsonResponse; class TestMiddleware implements MiddlewareInterface { public function process(ServerRequestInterface $request, DelegateInterface $delegate) { return new JsonResponse(['a' => 'b']); } } 

But then, how to make them work together to return

[ 'a' => 'b', 'c' => 'd', ]