I had this same issue when I was starting out and all I had done was miss the starting @ off the package name.

So npm -i primeng

this caused the forced github login prompt

But npm -i @primeng

This was what I meant to type and worked as expected but because I was a n00b I didn't notice I'd missed off the @ symbol.

So....

• npm -i packagename : WRONG
• npm -i @packagename : RIGHT