title: Pushing to private nuget feed Prompts for Credentials
body: <p>I have set up a private nuget feed using a empty web application and the nuget server package. It is all working, I can retrieve from the feed, and I can publish to the private feed using the Nuget Package Explorer. 
  But I cant publish via the command line - it prompts for credentials. I have set the ApiKey in the web application in the Appsettings, to a simple password, and I have tried adding the ApiKey to the push command. This Prompts me for a username and then a password.
  I have also tried the SetApiKey command but I get the same behavior.
  On the build server I am trying the same thing with the same results.</p>
  
  <p>Here is the error messages from the build Log (identifying info x'd out)</p>
  
  <pre><code>nuget pack "C:\Builds\2\OE Phase II\Common\src\WebApi\Web.Http\Bxxxxxxxs.Web.Http.csproj" -IncludeReferencedProjects -Properties Configuration=Release
    nuget SetApiKey Bxxxxxxx1 -Source http://tfs12.xxxxxxxrps.com/Nuget
    nuget push *.nupkg -s http://tfs12.xxxxxxxrps.com/Nuget/
    C:\Builds\2\OE Phase II\Common\bin\xxxxxxx.Web.Http.dll
    1 File(s) copied
    Attempting to build package from 'xxxxxxx.Web.Http.csproj'.
    Packing files from 'C:\Builds\2\OE Phase II\Common\src\WebApi\Web.Http\bin\Release'.
    Using 'xxxxxxxs.Web.Http.nuspec' for metadata.
    Found packages.config. Using packages listed as dependencies
    Successfully created package 'C:\Builds\2\OE Phase II\Common\bin\xxxxxxxs.Web.Http.1.0.0.0.nupkg'.
    The API Key 'xxxxxxx' was saved for 'http://tfs12.xxxxxxxrps.com/Nuget'.
    Pushing Bxxxxxxxrs.Data 1.0.0.0 to 'http://tfs12.xxxxxxxrps.com/Nuget/'...
    Please provide credentials for: http://tfs12.xxxxxxxrps.com/Nuget/
    Object reference not set to an instance of an object.
    UserName: Password: 
  </code></pre>