As of now, PSR-15 middlewares are available in the current master of Flow Framework. They should povide an easy means to adapt the request handling of your application, by making use of existing PSR-15 middlewares easily (e.g. https://github.com/middlewares/awesome-psr15-middlewares). This also means that your existing custom
Http Components will eventually not be supported any more. It is still not clear if this already happens with the next major (7.0 ~ end of the year) or if we postpone the removal of the components to give more time to adapt.
In the next months, we will start converting the existing Flow components to middlewares where it makes sense and is easily doable. You can follow progress at https://github.com/neos/flow-development-collection/issues/2019
Documentation for the feature should be available latest by tomorrow at https://flowframework.readthedocs.io/en/latest/TheDefinitiveGuide/PartIII/Http.html#middlewares-chain
Take a look and please provide any feedback here or on slack you have on where you struggle with getting middlewares to work as you expect, or have issues with understanding how to use them.