HttpClient currently only supports Basic authentication but the cache maintains a scheme property. Whether it is relevant to support multiple schemes in the cache when the HttpClient only supports Basic authentication out of the box should be reexamined. Another improvement that might be investigated would be to drop the synchronization for Cache::get and use a CopyOnWriteArrayList instead of the current LinkedList.
See http://mail.openjdk.java.net/pipermail/net-dev/2019-November/013257.html