If the TIBCO Spotfire Server requires a proxy to access the internet then it's possible to configure this via JVM options.
Please refer to the document How do I change JVM heap size and parameters for TIBCO Spotfire server
for the process to alter JVM parameters.
The following JVM parameters will configure a proxy.
-Dhttp.proxyHost -Dhttp.proxyPort -Dhttps.proxyHost -Dhttps.proxyPort
For example if the proxy host is 192.168.1.1 and the port is 8080 the configuration would look like:
Restart the service to make this effective.