Hey there,
It is mentioned in the first post on this topic:
from server console run:
cd /var/discourse
./launcher enter app
rails c
irb > SiteSetting.enable_sso = false
irb > SiteSetting.sso_url = "https://www.example.com/sso"
irb > SiteSetting.sso_secret = "Your_secret_token"
irb > exit
exit
Cheers