It this possible? How? (Maybe silly question, but I couldn't find answer :( )
EDIT:I am using Openfire server embedded into different system, so I need if admin of the system kicks out the user from the system server, user's connection to Openfire server should be closed too.
Under some cases, yes :
The same full jid "user@host/resource" connects from two different sources. The server usually disconnects the old one. Though some servers (OpenFire comes to mind) may make it configurable.
If a client has admin right, using adhoc commands, it can destroy another connection. It depends on the server implementation. (ejabberd makes that possible)
In all other cases, clients are isolated and this can't happen. (Or it's a high priority bug in the server).
In the Openfire admin console, running as an HTTP server on port 9090, the administrator can disconnect any connected client.