Regardless, if I attempt to use org.apache.http.osgi.services.ProxyConfiguration and associated org.apache.http.osgi.services.HttpClientBuilderFactory within a vanilla 6.2 instance I see that the username, even tho it's set in the Web Console config, is ignored (an empty string is used when debugging the code).
I've got a local squid proxy set up. If I use that without auth everything is fine and I see requests from AEM logged to /var/log/squid/access.log. If I setup auth on proxy server (verifing it works using a browser) then use AEM provided HTTP client it fails... must be due to the above.
I don't have this problem in 6.3. The username is logged out as expected as are requests to the proxy get through.