Documentation for Crowd 1.0. Documentation for other versions of Crowd is available too.
If your directory is not listed in 1.1.1 Supported Applications and Directories then you will need to create your own custom directory connector.
Custom directory connectors allow developers to connect Crowd to custom user-stores, such as existing databases or legacy system.
Full Javadoc for the RemoteDirectory
interface can be found here: http://docs.atlassian.com/crowd/current/com/atlassian/crowd/integration/directory/RemoteDirectory.html.
After creating your directory connector, please see 2.2.3 Configuring a Custom Directory Connector.