Documentation
Configuration / CakeAuthenticator.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 Cake PHP user session key
// Change the user key too look for
$moxieManagerConfig['CakeAuthenticator.user_key'] = 'user';
// User specific path in moxiemanager/config.php
$moxieManagerConfig['filesystem.rootpath'] = 'users/${user}';
Override the user by setting:
// Override user
CakeSession::write("user", "someuser");