I need to install npm private packages during provision.
But they require `npm login` execution before installing private packages, otherwise npm will not find any priate package.
Because provision is not interactive, even if I run `npm login` during provision then I can't specify username and password.
So how to manage it?
I would avoid to put in the Vagrant machine filesystem files coming from the host - e.g. containing credentials or tokens - because I assume the host has no npm installed.