.sa accounts in vCenter

I have a number of accounts in vCenter under home\administration\roles that are specified as such.  (My AD domain is contoso.local):

I know that the identity source that SSO is getting these accounts from is obviously active directory

contoso\administrators

contoso\operators

Then I have one account specified as such:

user1.sa

What is the identity source for an account with an ".sa" suffix?  Is that a local account on the Windows VM where SSO is installed?  Is it some other identity source?

Thanks!