docs: public ContextItems unmarshal(String marshaledContext, String authSignature) throws Exception {
          ContextItems contextItems = new ContextItems();
          contextItems.addItems(marshaledContext);
          String whichKey = contextItems.getItem(PROPNAME_KEY);
          String timestamp = contextItems.getItem(PROPNAME_TIME);
          
          if (authSignature != null && !signer.verify(authSignature, marshaledContext, timestamp, whichKey)) {
              throw new MarshalException("Invalid digital signature");
          }
          
          return contextItems;
      }