npm ERR! code E401 — Unauthorized Error

Use npm login or configure an authentication token.

# Login interactively
npm login

# Or use a token
npm set //registry.npmjs.org/:_authToken=YOUR_TOKEN

# For GitHub Packages
npm set //npm.pkg.github.com/:_authToken=YOUR_GITHUB_TOKEN

Set up authentication for private registries in .npmrc.

# ~/.npmrc or project .npmrc
registry=https://registry.npmjs.org/
//registry.npmjs.org/:_authToken=${NPM_TOKEN}

# For scoped packages
@mycompany:registry=https://npm.pkg.github.com/
//npm.pkg.github.com/:_authToken=${GITHUB_TOKEN}

Ensure CI/CD environments have the NPM_TOKEN or similar env variable set.

# GitHub Actions example
- name: Install dependencies
  env:
    NPM_TOKEN: ${{ secrets.NPM_TOKEN }}
  run: npm ci

# The token is read from .npmrc that references the env variable