Spark useragent and proxy question

Hello,

we use Spark 2.5.8 and Openfire 3.6.4 for internal communications. But I want to ensure, that the users doesn’t use spark over our proxy to connect to foreign XMPP servers.

I can configure ACLs on our HTTP proxy Squid to deny access from defined useragents. Is spark using a useragent string?

And second question: Is it possible, that Spark isn’t using the HTTP proxy? I configured one, but it allways tries to connect directly and not over the proxy.

Regards,

Joe