Workaround for getting the uid / gid when only the 'username' is available. - Advantages: works without needing to compile a C++ addon - Disadvantages: need to be root to run it :(

userinfo.js

//-----------------------------------
// userinfo.js
//-----------------------------------

/**
 * Workaround for getting
 * the uid / gid when only
 * the 'username' is available.
 *
 * Works on POSIX ONLY (i.e. not Windows)
 */

var fork = require('child_process').fork
  , child;

exports.getUserInfo = function (username, groupname, cb) {
  if (2 === arguments.length) {
    cb = groupname;
    groupname = -1;
  }
  child = fork(__dirname + '/getuid');
  child.on('message', function (userInfo) {
    cb(null, userInfo);
  });
  child.on('error', cb);
  child.send({
      username: username
    , groupname: groupname
  });
};

//-----------------------------------
// getuid.js
//-----------------------------------

/**
 * Child process for the workaround
 * for getting user-info.
 */

exports.getUserInfo = function (user) {
  process.setgid(user.groupname);
  process.setuid(user.username);
  return {
      username: user.username
    , groupname: user.groupname
    , uid: process.getuid()
    , gid: process.getgid()
  };
}

process.on('message', function (userName) {
  process.send(exports.getUserInfo(userName));
  process.exit(0);
});