One fine day, someone came to me and asked, " I can't add domain users to vCenter. Can you help?" So, when I checked, I found this : So yes, no domain listed there. So when I asked in detail, it seems this was a new deployment, vCenter just being created. Which really helped me to narrow down to root cause. Issues : Unable to Grant Permission to Domain ID - No Domain Listed Troubleshooting Login to vCenter using default admin ID ( [email protected] ). These steps shall be done from Web Console rather than vSphere Client. Click at Administration Click at Single Sign-On > Configuration . So as we can see here, only vSphere.local and vCenterServer (Default) are configured in Identity Sources. It means, these are the only domains which can be authenticated to. Resolution : Click at Add Identity Source. Depending on the environment, appropriately choose identity source type . For this example, it is Act