Workflow to check for Duplicate SAMAccount Name in multi-domain forest

Can someone point me in the right direction to create a workflow which upon create request will check to see if there is a user by that SAMAccount name already in the forest?

  • OOB ARS User Provision policy | generate User Logon - provides criteria check uniqueness of the generated user SAMAccountName against scope: (a) Domain, (b) Forest, (c) All Managed Domains. I assume (b) does not required to make all Domains in the Forest to be registered as Managed Domains in ARS.

    Aidar Karabalaev