A system component that is used to authenticate identities. This interface is provided to 
Services and other system components, and is used to authenticate identities within a specific context. Implementations of this interface use 
IdentityAuthenticators to actually perform authentication. 
 Note that the IdentityCoordinator provided to Services via the ComponentRegistry field of their constructor will only be able to authenticate identities within that Service's context. It is safe, however, to use that IdentityCoordinator in any context and outside of a running transaction. Services must not, however, use their IdentityCoordinator until ready is called, because before this point the underlying context is not valid and available to the IdentityCoordinator.