[lost_my_pwd]

One can also install modules from a git repo, from which access to the module can be controlled in the regular git fashion:

  "dependencies": {
    "private-module": "git+ssh://..."
  }

or:

  "dependencies": {
    "private-module": "git+https://<user>:<password>@..."
  }

If one chooses to use Github, there is also the option to use an auth token in the url scheme instead of needing to distribute an SSH PK (bad) or having login credentials in the package.json:

  "dependencies": {
    "private-module": "git+https://<token>:[e-mail]/<account>/<repo>.git"
  }

One could also just have a folder of private modules mounted from some shared file server or whatever. An NPM server is not an absolute requirement to use npm.