var ADMIN_USER = 'root';
var ADMIN_PASS = 'ass4' + ADMIN_USER
var NEW_USER = 'dummy';
var TARGET_DB = 'mydb';

var conn = new Mongo();
var admDb = conn.getDB('admin');
try {
	admDb.createUser({user: ADMIN_USER,
                    pwd: ADMIN_PASS,
                    roles: [{role: 'userAdminAnyDatabase', db: 'admin'}]});
} catch (err) {
	if (/not authorized/.test(err.message)) {
		admDb.auth({user: ADMIN_USER, pwd: ADMIN_PASS});
	} else {
		throw err;
	}
}

var db = conn.getDB(TARGET_DB);
if (! db.getUser(NEW_USER)) {
	db01.createUser({user: NEW_USER,
                   pwd: 'ass4' + NEW_USER,
                   roles: [{role: 'readWrite', db: TARGET_DB}]});
}