code: @ReadOperation
      public Map<String, Object> handle() {
          val model = new HashMap<String, Object>();
  
          val diff = Duration.between(this.upTimeStartDate, ZonedDateTime.now(ZoneOffset.UTC));
          model.put("upTime", diff.getSeconds());
  
          val runtime = Runtime.getRuntime();
          model.put("totalMemory", FileUtils.byteCountToDisplaySize(runtime.totalMemory()));
          model.put("maxMemory", FileUtils.byteCountToDisplaySize(runtime.maxMemory()));
          model.put("freeMemory", FileUtils.byteCountToDisplaySize(runtime.freeMemory()));
  
          val unexpiredTgts = new AtomicInteger();
          val unexpiredSts = new AtomicInteger();
          val expiredTgts = new AtomicInteger();
          val expiredSts = new AtomicInteger();
  
          val tickets = this.centralAuthenticationService.getTickets(ticket -> true);
          tickets.forEach(ticket -> {
              if (ticket instanceof ServiceTicket) {
                  if (ticket.isExpired()) {
                      this.centralAuthenticationService.deleteTicket(ticket.getId());
                      expiredSts.incrementAndGet();
                  } else {
                      unexpiredSts.incrementAndGet();
                  }
              } else {
                  if (ticket.isExpired()) {
                      this.centralAuthenticationService.deleteTicket(ticket.getId());
                      expiredTgts.incrementAndGet();
                  } else {
                      unexpiredTgts.incrementAndGet();
                  }
              }
          });
  
          model.put("unexpiredTgts", unexpiredTgts);
          model.put("unexpiredSts", unexpiredSts);
          model.put("expiredTgts", expiredTgts);
          model.put("expiredSts", expiredSts);
  
          return model;
      }
docs: Gets availability times of the server.
  
  @return the availability