EAP chaining is just a method of how client perform 802.1x authentication which has nothing to do with which user database you use. Can you provide more specific information as far as which client OS you plan to use, and how it will perform machine authentication? What I am trying to get to is, if this is a Windows domain computer, the machine auth will occur automatically and the credential is known only between the machine and AD. But if this is something else, I am not sure how it will look up machine account in the LDAP database.