I'm sorry to inform you that it isn't possible to connect an Active Directory to an OnDeamdn instance because this is one of the restricted functions in OnDemand: https://confluence.atlassian.com/display/AOD/Restricted+Functions+in+Atlassian+OnDemand
However, you can integrate your OnDemand instance with Google Apps and that allows you to configure a Single Sign-On solution but that is the only SSO option for OnDemand customers.
All the best,
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