SSO implementation in community edition
First of all I want to highlight that SSO (with CAS, SAML or Kerberos-Windows) is a native feature of Bonita Enterprise Edition. Still it should be doable to implement it and Community Edition. For that you probably want to start reading the documentation page about user authentication.
Synchronization between AD and Bonita is also a feature of Bonita Enterprise Edition. This rely on a component that synchronize Bonita organization with users information store in AD.