Execution jnlp file

Hi, I hope someone can help me get the launch of a xxxx.jnlp file from proxy users to work. My situation is this on a site I have users who can connect via the web with authentication only via proxy (Forigate 201E firewall ip) and a rule is created in the firewall rules that blocks direct access to http and hhtps services. The sites to which the jnlp file refers are xxxx.sicraweb.it:443. My problem is that when I launch the jnlp file it freezes the execution of the file. Can anyone kindly tell me what I can implement or fix on the firewall to make this java application work? Thanks to all in advance.