[BUG] NPM Login Failure Blocking Package Installation

[bobbybeers]

Is there an existing issue for this?

• I have searched the existing issues

This issue exists in the latest npm version

• I am using the latest npm

Current Behavior

Incident: NPM Login Failure Blocking Package Installation

Summary

Unable to install packages from private registry due to npm login failing with "Exit handler never called!" error.

Severity

High - Blocks package installation and updates

Symptoms

1. Package install returns E401 - Incorrect or missing password
2. npm login fails with:

npm error Exit handler never called!
npm error This is an error with npm itself.

3. Browser-based auth flow never completes

Root Cause

Known npm CLI bug where exit handler fails during SSO/browser-based authentication with private registries. Auth token is never saved to .npmrc.

Workaround

Manually generate access token via registry web UI and add to .npmrc:

Expected Behavior

Running npm login should open a browser window, complete SSO authentication, and save the auth token to .npmrc, allowing subsequent package installations to succeed.

Steps To Reproduce

1. Run npm login against a private registry using browser-based SSO authentication
2. Press ENTER when prompted to open browser
3. Observe "Exit handler never called!" error before browser auth can complete
4. Attempt to install a package from the private registry
5. Receive E401 - Incorrect or missing password error

Environment

• npm: 10.8.2
• Node.js: v20.18.3
• OS: macOS 26.1
• System: Mac