On the Zend Framework blog Matthew Weier O'Phinney has posted another tutorial, this time showing you how to use nested middleware in Expressive allowing for the composition of your own workflow in the request/response flow.
A major reason to adopt a middleware architecture is the ability to create custom workflows for your application. Most traditional MVC architectures have a very specific workflow the request follows. While this is often customizable via event listeners, the events and general request lifecycle is the same for each and every resource the application serves.
With middleware, however, you can define your own workflow by composing middleware.
He starts by describing one of the main concepts in the workflow of the application: pipelines. He gives an example of the default pipeline included with the Expressive skeleton application and how the middleware it uses nests to create a custom logic and handling flow. He follows this with an example scenario showing how to add authentication into the pipeline, specifically the use of Digest authentication via a PSR7 middleware package. Code is included for the integration of this package and the end result - all pages requiring authentication. He shows how to modify this and limit it to only certain paths and how to nest them in the route definitions.
Finally he shows another approach - creating a custom middleware pipeline inside of the factory for the requested middleware. He also covers nested applications, using traits for common workflows and the use of "delegator factories".