ModActiveDirectory is a project mainly written in PHP, it's free.
ActiveDirectory integration into MODx Revolution
This is an ActiveDirectory integration for MODx Revolution.
Simply install via Package Management in MODx Revolution.
From there, you'll need to setup some settings:
modActiveDirectory will automatically grab all the ActiveDirectory groups a user belongs to, and then search for any MODx UserGroups with matching names. If found, the user will be added to those groups.
If you'd like to disable this, set the activedirectory.autoadd_adgroups System Setting to 0.
modActiveDirectory also allows you to specify a comma-separated list of MODx UserGroup names to automatically add the User to. This can be set in the activedirectory.autoadd_usergroups setting.
Make sure you give the User Groups the User will auto-join access to the manager (through Access Controls), should you want your ActiveDirectory users to have mgr access.