* Participant in processing a server request and response.
* An HTTP middleware component participates in processing an HTTP message:
* by acting on the request, generating the response, or forwarding the
* request to a subsequent middleware and possibly acting on its response.
* Process an incoming server request.
* Processes an incoming server request in order to produce a response.
* If unable to produce the response itself, it may delegate to the provided
* request handler to do so.
public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface;