I'll start with the easy one; connectors are "read only", there is no mechanism to push a package to a connector in ProGet.
As for authentication, I really don't know. That's weird, and it's definitely nothing in ProGet.
The 401 could be coming from a proxy server (inside your network) or from registry.npmjs.org itself, and there's no way to know within ProGet which it is.
I can't imagine it's a proxy server that somehow works with a npmjs.org username/password. But, maybe it is.
I don't know why registry.nmpjs.org would send you a 401. Other users haven't experienced this, and I just tested it on a brand new instance myself... and the connector worked just fine. There is talk of throttling large organizations, so maybe it's related to them blocking your IP or something?
It could have also just been a temporary glitch, somewere. Maybe if you remove authentication, it will work.
ABout the only way to diagnose this would be to attach ProGet to a tool like Fiddler or WireShark, so you can see the requests PRoGet makes, then reproduce those exact same requests, and either reach out to your internal IT folks or try your luck with npmjs.
