title: NuGet restore using 2 sources with and without http proxy
body: <p>In our company we are behind HTTP proxy, so we need to use it when accessing nuget.org to restore packages.</p>
  
  <p>We also use an internal NuGet server where we publish some shared components packaged as NuGet.</p>
  
  <p>When running CI build we want to restore packages from both sources. Is there any way to configure NuGet to use proxy for one but not the other?</p>
  
  <ul>
  <li>global nuget.org - using proxy</li>
  <li>internal NuGet server - not using proxy, directly</li>
  </ul>
  
  <p>If I define a http_proxy in NuGet.config it's used for both sources, hence failing with the internal one.
  If I don't define it, it fails with global source.</p>