How to detect diff domain user status online/offline?

Hello, I’m try to implements a chat bot plugin, and one of requirement is when customer on domain A ask “bring me some staff of custom-service”, plugin will query online staff on domain B and send back list.
I have two servers with two diff domains, let’s say domain A and domain B. And I can send message cross domain A and domain B.
I have review code on github, DefaultUserProvider.java in line 87, it just simple throw exception with message “Cannot load user of remote server” when JID is diff domain.
How can I detect online status which user on other domain in openfire plugin?

Thank you!