system.clj

(defrecord RingHandler
  [handler injections app]

  component/Lifecycle
  (start [this]
    (if app
      this
      (let [app (fn [req]
                  (let [injectables (select-keys this injections)]
                    (handler
                      (if (empty? injectables)
                        req
                        (apply assoc req (apply concat injectables))))))]
        (assoc this :app app))))
  (stop [this]
    (if this
      (dissoc this :app)
      this)))

(defn new-ring-handler
  ([handler]
   (new-ring-handler handler nil))
  ([handler injections]
   (map->RingHandler {:handler http
                      :injections injections})))