Recently I ran into a scenario where a CMS site would not use the SAML login authentication for page access. The ServiceNow Wiki had the answer (and thank you my homies Sean Barrett and Ben Yukich for sharing). In case you find the answer here on the community first - I can lead you to the answer.
From the Wiki:
Since public pages do not require login, and CMS sites are public by default, CMS pages do not use SSO. To configure CMS to use SSO, make the view_content page private.
To turn off public-facing content pages and enable SSO:
- Navigate to Public Pages (sys_public.list)
- For the view_content page, set Active to false.
http://wiki.servicenow.com/index.php?title=Content_Management_Security#CMS_Sites_and_Single_Sign-On_...
