Cerner External Flag Provisioning

For our Cerner integration, we want to provision an attribute that indicates whether the user is an external user or coming from the source HR system. We reviewed the documentation at Account Attributes for a list of the attributes in the account schema and did not find any external flag, although the directoryIndicator attribute comes close. Could anyone provide feedback on how to best approach this?

You can have additional Identity Attribute with first valid transform as
If Account source == HR then Internal else external