add doc for middleware usage in "dispatch" event

doc/book/cookbook/using-middleware-in-dispatch-event.md

@@ -0,0 +1,46 @@
+# Using Middleware in "dispatch" Event
+
+During Mvc Workflow, you can use the Middleware in 'dispatch' event by provide `Psr7Bridge`. For example, you have `AuthorizationMiddleware`:
+
+```php
+namespace Application\Middleware;
+
+class AuthorizationMiddleware
+{
+    public function __invoke($request, $response, $next = null)
+    {
+        // handle authorization here...
+    }
+}
+```
+
+As the request and response in 'dispatch' event is a `Zend\Http` Request and Response object, we need the bridge to convert into PSR-7 Request and Response, and then, the result of invoked `AuthorizationMiddleware` above needs to be converted to `Zend\Http` Response if an instance of `Psr\Http\Message\ResponseInterface`. To do that, you can do the following:
+
+```php
+namespace Application;
+
+use Application\Middleware\AuthorizationMiddleware;
+use Psr\Http\Message\ResponseInterface;
+use Zend\Psr7Bridge\Psr7ServerRequest;
+use Zend\Psr7Bridge\Psr7Response;
+
+class Module
+{
+    public function onBootstrap($e)
+    {
+        $app          = $e->getApplication();
+        $eventManager = $app->getEventManager();
+        $services     = $app->getServiceManager();
+
+        $eventManager->attach('dispatch', function ($e) use ($services) {
+            $request  = Psr7ServerRequest::fromZend($e->getRequest());
+            $response = Psr7Response::fromZend($e->getResponse());
+            $result   = ($services->get(AuthorizationMiddleware::class))($request, $response, function() {});
+
+            if ($result instanceof ResponseInterface) {
+                return Psr7Response::toZend($result);
+            }
+        }, 2);
+    }
+}
+```

doc/book/middleware.md

@@ -27,7 +27,7 @@ a "controller" in the routing defaults, you provide "middleware":
 ```php
 // Via configuration:
 return [
-    'router' => 
+    'router' =>
         'routes' => [
             'home' => [
                 'type' => 'literal',

mkdocs.yml

@@ -14,6 +14,8 @@ pages:
       - Examples: examples.md
       - 'Dispatching PSR-7 Middleware': middleware.md
       - 'Migration Guide': migration.md
+    - Cookbook:
+      - 'Using Middleware in "dispatch" Event': cookbook/using-middleware-in-dispatch-event.md
 site_name: zend-mvc
 site_description: 'zend-mvc: MVC application provider'
 repo_url: 'https://github.com/zendframework/zend-mvc'