It seems like you are referring to the default identity provider that is set up for Directory Server which is connected to AD in the current domain. Previously, in LM 8.3, no default provider was set up out of the box.

Directory Server uses Windows Authentication through IIS to authenticate with the AD server. The authentication uses Kerberos by default, but falls back to NTLM.

As a note, this means that if you (a) have not configured the Directory Server service use as a Kerberos SPN and (b) perform an action that access AD from a machine other than the machine where Directory Server is installed, you will be prompted to enter your Windows Credentials.