ZendAuthenticator.user_key

This enables you to specify the key to look for in the sessions to override the user variable. The ${user} will be replaced in all config options if you set the CodeIgniter PHP user session key

// Change the user key too look for
$moxieManagerConfig['ZendAuthenticator.user_key'] = 'user';

// User specific path in moxiemanager/config.php
$moxieManagerConfig['filesystem.rootpath'] = 'users/${user}';

Override the user by setting:

// Override user in using Zend 2
$this->session = new Zend\Session\Container();
$this->session->user = "username";