[BUG] npm can't pick up PAC file for proxy auto-configuration

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

In the organization I work at, for security reasons, to connect to the outside internet there's an HTTP proxy server in the middle configured with a PAC file. https://docs.microsoft.com/en-us/windows/win32/winhttp/winhttp-autoproxy-support

npm can't reach out to the registry without that configuration, so my workaround is to use a secondary reverse proxy locally, but that isn't the most optimal solution by any means.

Expected Behavior

npm should be able to pick up the pac file's location from IE's settings, read it, and use the appropriate proxy, using user default credentials if applicable (such as the case of an NTLM-based proxy server or one using Kerberos authentication).

Steps To Reproduce

1. Install an HTTP(S) proxy server that requires Kerberos authentication.
2. Restrict network connectivity so internet can only go through that proxy.
3. Run npm update -g
4. Wait for it to time out as it can't figure out that proxy.

Environment

• npm: 8.13.2
• Node.js: 16.15.1
• OS Name: Windows 10
• npm config:

null = ""
registry = "http://localhost:8080/"
strict-ssl = true

Start by tracing the proxy configuration used when running npm update -g on Windows, then investigate how the PAC file location from IE settings and WinHTTP auto-proxy support could be used. Reproduce with a Kerberos-authenticated proxy and restricted internet access; done means npm selects the PAC-provided proxy and authenticates with the user's default credentials.