To access the internet server needs to use an authenticated proxy server.
Details for proxy server and login account are entered and work in other areas of Moodle.
If an attempt is made to add an Remote RSS Feed block it reports
Error loading this RSS feed (A feed could not be found at http://moodle.org/rss/file.php/1/1/forum/1/rss.xml. A feed with an invalid mime type may fall victim to this error, or SimplePie was unable to auto-discover it.. Use force_feed() if you are certain this URL is a real feed.)
The file /lib/simplepie/moodle_simplepie.php mentions using Moodle cURL
"By using the moodle curl class we ensure that the correct proxy configuration is used."
But there appears to be no further customisation to use the proxy settings.