NPM behind NTLM proxy
Rather than running CNTLM, you could instead try running Fiddler when you need to use npm. I've found this works in fairly locked down environments (e.g. investment banks). It's also a tool that is fairly easy to make a business case for (if you need to) since it's invaluable for checking/creating/altering HTTP traffic.
I've had to go this route before due to usage of smartpass authentication - i.e. we didn't actually have passwords. At those locations setting up CNTLM would have been impossible.
CNTLM answer was working for me, but with connection errors make npm unusable. I've fixed them by adding this header in CNTML.
Header Connection: close
I solved it this way (OS: Windows XP SP3):
1. Download CNTLM installer and run it.
2. Find and fill in these fields in cntlm.ini. Do not fill in the Password field, it's never a good idea to store unencrypted passwords in text files.
Username YOUR_USERNAME
Domain YOUR_DOMAIN
Proxy YOUR_PROXY_IP:PORT
Listen 53128
3. Open console, and type these commands to generate password hashes.
> cd c:\the_install_directory_of_cntlm
> cntlm -H
Password: ...type proxy password here...
PassLM D6888AC8AE0EEE294D954420463215AE
PassNT 0E1FAED265D32EBBFB15F410D27994B2
PassNTLMv2 91E810C86B3FD1BD14342F945ED42CD6
4. Copy the above three lines into cntlm.ini, under the Domain field's line. Once more, do not fill in the Password field. Save cntlm.ini.
5. Open the Service Manager (from command line: services.msc), and start the service called "CNTLM Authentication Proxy".
6. In the console, type these lines:
> npm config set proxy http://localhost:53128
> npm config set https-proxy http://localhost:53128
> npm config set registry https://registry.npmjs.org
7. Now npm view, npm install etc. should work. Example:
> npm view qunit
...nice answer, no errors :)
Another alternative is to use Px for Windows which talks NTLM on your behalf like Cntlm and NTLMAps without having to provide your credentials. It uses the logged in user's credentials via SSPI.