I stand corrected.
I downloaded the most recent source code for the plugin on github and found the following that I needed:
This is the AUTHENTICATION keys I needed (I used http.proxyUsername) when, in fact, it is “http.proxyUser”.
System.setProperty(“http.proxyUser”, StringUtils.defaultString(activeProxy.getUsername(), “”));
System.setProperty(“http.proxyPassword”, StringUtils.defaultString(activeProxy.getPassword(), “”));
This would have been the only information I needed in this correspondence.