Bootstrap Windows with Proxy - "Failed download: download completed, but downloaded file not found"

Update again, for those following along or who encounter this in the future

ERROR: No response received from remote node after 2.37 minutes, giving up.
ERROR: Exception: Unable to parse authorization header. Headers: {"Proxy-Authenticate"=>"NTLM", "Cache-Control"=>"no-cache", "Pragma"=>"no-cache", "Content-Type"=>"text/html; charset=utf-8", "Proxy-Connection"=>"close", "Set-Cookie"=>"BCSI-CS-477914e091836061=2; Path=/", "Connection"=>"close", "Content-Length"=>"1106"}
Body:

Access Denied

Your credentials could not be authenticated: "General authentication failure due to bad user ID or authentication token." You will not be permitted access until your credentials can be verified.

This is typically caused by an incorrect username and/or password, but could also be caused by network problems.

If you have any questions please contact desktopsupport@blah.com

That looks like I'm reaching the proxy but the authentication is just failing so I think I'm close. I found this page - Working with Proxies - which makes reference to updating your knife.rb to include these entries

http_proxy          myproxyip:proxyport
http_proxy_pass     mywindowscredsforproxy
http_proxy_user     mywindowspass

Our proxy uses NTLM I think so its just a matter of formatting at this point. I'm working with our networking team that manages the proxy but I think once I get it added to knife.rb correctly, we should be in business. Once I get it working I plan on recapping the exact changes here for everyone's sake in the future.