Edited Issue: Cannot restore packages from secured feed without write permissions on global nuget.config [3164]

Example scenario which is currently unsupported:
*NuGet package restore from a secured package source during deployments to Windows Azure Web Sites is impossible.*

## Why?
* Encrypted package source credentials are machine bound / non-portable
* Kudu process does not have write permissions on `%appdata%\nuget\nuget.config` (likely because of shared environment)
* Kudu process is running impersonated or without user profile loaded, which makes nuget.exe throw a CryptographicException during password encryption
* No support for passing in -Username / -Password to nuget.exe install command
* [My pull request][1] to support clear-text credentials in local nuget.config is still under review :-)

__Edit__, the following is no longer applicable as the new -ConfigFile command option fixed this:
* <strikethrough>Storing encrypted package source credentials only supports `%appdata%\nuget\nuget.config` (no way to target a local config for on-the-fly encrypting & storing of credentials)</strikethrough> (just fell in love with the codeplex rich editor here...)

I can't find any working approach to support this scenario with the current version of NuGet.

[1]: http://nuget.codeplex.com/SourceControl/network/forks/XavierDecoster/NuGet2991/contribution/4018