Any offical method to mirror packages.microsoft.com ?

# Issue Title

Is there any methods to mirror the .NET Core packages source (packages.microsoft.com) ?

# General

I have a isolated environment without internet access but sometimes need .NET Core SDK and runtime.
Searched in the docs but not found anything about mirroring the offical package source.
Of cource I can use `wget --mirror` command to crawl the whole site, but I'm still looking for better way or the offical way to do it, like a lot package source provide `rsync` or `ftp`.