How to set private NPM registry for JupyterLab installs?

Can someone explain the steps that a user may take to set a private NPM registry for JupyterLab installs?
We created an extension for JupyterLab and there are some private NPM packages in it when i try to build jupyterlab with this extension it returns an error that Couldn’t find package.

Can someone help?

I found a workaround by copying .npmrc file to jupyterlab/staging folder