Crowd ignores networking system properties

There has been a few support cases being raised because users are not able to connect to an external User Directory using a outbound proxy.
https://support.atlassian.com/browse/SSP-6341

A stash defect has been raised because of this restriction.
https://jira.atlassian.com/browse/STASH-5501

Steps to reproduce

1. Set up Stash using an outbound proxy. Stash is set to go through Charles proxy setup in the same machine with the following parameter, nonproxyhost is unset to force all connection through the proxy:

   -Dhttp.proxyHost=localhost -Dhttp.proxyPort=8888 -Dhttps.proxyHost=localhost -Dhttps.proxyPort=8888

2. Add a Crowd Directory in Stash

Expected Results

The request should go through the outgoing proxy set

Actual Results

The request bypasses the proxy. This is proven by the absence of the request from Charles proxy logging. All other connection such as UPM and Application link goes through the proxy, as in Charles proxy logs: