Single Sign-On setup

I had been tinkering with Single Sign-On via AD on our FortiGate 300D for a while and had it working just fine.  It was a very simple configuration that allowed a particular AD user access to a particular network.

Then we upgraded for FortiOS 6.0 and everything stopped working. 

In attempting to fix the problem I have discovered that one of the settings referred to in all the Fortinet documentation is not visible on ANY of my firewalls (all FortiOS 6.0)...there is no longer any "Singe Sign-On" entry under "User & Device"

...what am I missing?

Thanks