Extensibility model for package download

[dtivel]

This request is from VSTS.

1. A mechanism for providing custom package download implementation through a plugin.
2. A plugin must run in a process separate from NuGet tools.

The primary motivation is to provide alternate forms of package transmission.

CC @jmyersmsft

[maartenba]

Is there a spec for this somewhere?

[jmyersmsft]

Details are still in progress, but it's here: https://github.com/NuGet/Home/wiki/NuGet-Package-Download-Plugin

[maartenba]

Thanks!