Guacamole's SSO extensions are available separately from the main guacamole.war. The link for this and all other officially-supported and compatible extensions for a particular version of Guacamole are provided on the release notes for that version. You can find the release notes for current versions of Guacamole here: http://guacamole.apache.org/releases/.

The SSO extensions are packaged together in a .tar.gz file containing one extension for each supported SSO method:

SSO MethodExtension
CAScas/guacamole-auth-sso-cas-1.5.5.jar
OpenID Connectopenid/guacamole-auth-sso-openid-1.5.5.jar
SAMLsaml/guacamole-auth-sso-saml-1.5.5.jar