It is quite easy to add vCenter 6.7 to Active Directory or add AD as an identity source.
Assuming you have vCenter 6.7 installed on a new windows host like I have, the following is all that is required:
Click on Menu, then Administration, then configuration and then the Identity Sources tab
This will bring you to the screen above which lists the available identify sources. This is typically the vsphere.local system domain and the local OS in my case the host name is Dartagnan.
Click Add Identity Source which brings up the screen above. As I will be adding Active Directory and the underlying host running vCenter is windows 2016 this is quite easy. The Identity source type is already pre-populated with the type I need and the domain name is correct. I simply have to click OK.
From the screen above I can see that my new identity source has been created successfully.
If you were to try and log in now without doing anything further, the following error would be shown:
Unable to login because you do not have permission on any vCenter Server Systems connected to this client.
Before we can proceed, we need to add some domain users or groups to vCenter.
In this case I am going to add Domain Admins to the Administrators group within vCenter.
Click on Users and Groups on the left hand side and it will display the list of groups. Scroll down and click on Administrators.
Click Add Members
Select the Active Directory domain from the list, in my case its home.lab.
Type something in the search box and it will return suggestions. In my case I am adding the domain group Domain Admins.
Then click OK
Log out and you should now be able to log in with your domain user and have full admin rights.