dynamically create databases. help from http://jxcore.com/mongodb-2-6-with-jxcorenode-js-creating-admin-regular-users/

dynamic-db.js

var MongoClient = require('mongodb').MongoClient,
    Server = require('mongodb').Server,
    Db = require('mongodb').Db,
    ReplSetServers = require('mongodb').ReplSetServers;

var url = 'MONGODB_URI';

// You can connect to any database here. Likely whichever connection you want to be persistent
MongoClient.connect(url, function(err, uriDb) {
  if(err) console.log(err);

  var replSet = new ReplSetServers([
    new Server('HOST1', PORT1),
    new Server('HOST2', PORT2)
    ]);

  // Construct new DB "foo"
  var fooDb = new Db('foo', replSet, {safe: true});

  // Establish connection to new DB "foo"
  fooDb.open(function(err, db) {
    // Get to the admin database
    var adminDb = db.admin();
    // Authenticate by way of the admin database
    adminDb.authenticate('adminUser','adminPass', function(err, result) {
      // Add new user to the new DB "foo"
      db.addUser('user1', 'pass1', {"roles": ["readWrite"]},function(err, result) {
        // Authenticate on "foo" database
        db.authenticate('user1', 'pass1', function(err, result) {
          // Do queries to test connection
          var coll = db.collection('coll');
          coll.insert({"doc": "test"}, function(err, result){
            if (err) throw err;
            coll.find({}).toArray(function (err, docs) {
              if(err) throw err;
              docs.forEach(function (doc) {
                console.log(doc);
              });
            });
          });
        });
      });
    });
  });
});