In our organization, the enterprise user credential repository is stored in the corporate LDAP directory (MS Active Directory). Oracle E-Business Suite uses OID (Oracle's LDAP) Implementation to integrate with MS Active Directory (Microsoft's LDAP Implementation). However, external users and vendors who use Applications such as iSupplier and Procurement will continue to get authenticated using the local oracle database table, because of the fact that they are not enterprise users.
All the details are available in the Proof-of-Concept architecture diagram attached above.Click on it for the full-sized image. Currently i am still working on the Proof-of-Concept setup before finalizing the final architecture. The final architecture will have advanced features such as High Availability through Real Application Clusters for the OID database, OID LDAP Replication, Oracle AS Cluster for SSO login servers etc.