XIFF client through proxy

Hello guys!

I am working in a Jabber client using Xiff. We want that client to connect through a proxy because, in some cases the user could be behind a firewall and can only get access through proxy. So the question is:

Does XIFF have any support to implement this functionality? Maybe I am wrong in the way I am thinking the solution, please let me know!

Tnks in advance!