Update a value in a project's .npmrc

npm config will prefer to use the user-local .npmrc (i.e. ~/.npmrc). We can repurpose the --userconfig flag to write to an arbitrary file (e.g. an .npmrc stored in a project) instead:

npm config set key value --userconfig .npmrc

This can be useful in CI scenarios:

- name: Configure NPM_TOKEN
  run: npm config set '//npm.pkg.github.com/:_authToken' "${NPM_TOKEN}" --userconfig .npmrc
  env:
    NPM_TOKEN: ${{ secrets.NPM_TOKEN }}
- name: Install dependencies
  run: npm ci
- name: Remove NPM_TOKEN config
  run: npm config delete '//npm.pkg.github.com/:_authToken' --userconfig .npmrc

Source: stackoverflow