public RequestLogger(AppFunc next, LogManager logManager)
        {
            if (next == null) throw new ArgumentNullException("next");
            if (logManager == null) throw new ArgumentNullException("logManager");

            _next = next;
            _log = logManager.CreateLogger();

            _keys = new[]
            {
                "owin.RequestPath",
                "owin.ResponseStatusCode",
                "owin.RequestQueryString",
                "owin.RequestMethod",
                "owin.RequestScheme",
                "owin.RequestPathBase",
                "owin.RequestProtocol",
                "server.User",
                "server.RemoteIpAddress",
                "server.RemotePort",
            };
        }