A. Authentication is a service offered by the local computing platform to the application it is hosting. The application uses this service to authenticate users with a local LDAP.

B. Authentication is a service offered by the enterprise security framework. Applications access it directly, bypassing local platform security. The authentication service provides a level of abstraction between applications and the various instances of infrastructure (LDAPs, databases) that can be used to verify credentials.

C. Authentication is a service offered by both the local computing platform and the enterprise security framework. The local platform can be configured to direct requests to local LDAPs or common enterprise services, depending on the operating environment (dev/test/production). Meanwhile, the enterprise security framework services can virtualize several shared credential stores into a single shared service.

D. Authentication is not a valid example of a security service.