moved to Orchestrator community.
To your issue: Can you try to use a different syntax when providing the username?
Thanks for the quick reply. When I successfully authenticate on the Test Login page, both firstname.lastname@example.org and user@domain work (domain\user doesn't). From the client, user@domain and domain\user both produce "unknown user" errors in the log:
ERROR [VcoFactoryFacade] Unable to login (Ex: javax.security.auth.login.LoginException: Cannot login user : domain\user, user unknown)
This issue is now resolved. I added our AD identity source to the list of Default Domains via the vSphere web client in "Administration - Sign-On and Discovery - Configuration". I then restarted the vCO Configuration server and vCO Server in teh Orchestrator Configuration web console in "Startup Options". I was then able to log in via the Orchestrator client.