Answer to FB question

anothermodule.js

exports.i_do_something = function(options, callback) {
  var result = 'Here we go.';
  return callback(null, result);
};

auth.js

exports.check_has_permission = function(user, callback) {
  //do the work needed with the db to check user has permission for action
  var validated = your_actual_check();
  if (!validated)
    return callback(new Error('Authentication failed'));

  return callback(null, true);
};

route.js

var auth = require('./auth.js');

exports.web_function = function(req, res) {
  var user = req.params.user;
  
  return auth.check_has_permission (user, function(err, validated) {
    if (err) //failed auth
      return res.end('error: ' + err);
    
    //passed auth  
    var _module = require('your external module');
    return _module.i_do_something({/* want to pass anything? */}, function(err, result) {
      if (err)
        return res.end('error: ' + err);
      
      return res.end('OK: ' + result);
    });
  }); 
};