How to sign out?

We are using STS to log into Sitefinity and I can't figure out how to log out.

User hits stsexample.com and it uses Windows Authentication to create the claim and redirect the user to example.com (a SF instance).  

I have read the following links and cannot figure out how to log out:

docs.sitefinity.com/for-developers-authentication-sign-out-api

www.sitefinity.com/.../signout-not-killing-sf-session

What am I doing wrong?  I think I need to handle the signout call in the stsexample.com site, but I've not figured that out. 

Anything?