The Plone's features page stipulates in the "Authentication and Single Sign On" section:
Easy integration with LDAP, Active Directory, Oracle, OpenID, Shibboleth, CAS, Kerberos and many other authentication systems. You name it, Plone talks to it.
But I couldn't find any information about CAS. How could use it with a Plone 5.2 site?
There are lots of CAS plugins for Plone out here. I wrote one myself long time ago. Though for Plone 5.1 https://pypi.org/project/ftw.casauth/ looks like a good shot.