Proxy server authentication

Hi,

In order to use Docker in an enterprise it is most often required to access internet through a proxy server. Also in many cases that proxy server requires authentication to improve security.

In Docker for Windows beta 18 proxy support was added which is good. The issue is now that we need to add authentication information in clear text e.g.
http://userid:password@httpproxy.company.com:8080
and this is not good at all.
Either it should be configured separately with encryption or using credentials from Windows login (or even to support both alternatives)