I read the documentation about the Single-Sign-On for CUBA Applications and I understood that your mechanism uses custom HTTP-based protocol and currently does not provide integration with systems using standard authentication protocols like SAML or OIDC.
Do you have in plan to support in the future Service Providers which are not CUBA application?
You can implement service provider that will be compatible with the current protocol. But instead, I’d recommend that you try to implement custom login provider for cuba app with SAML, for instance, using Spring SAML - https://projects.spring.io/spring-security-saml
At the moment, we are not planning to build any IDP SSO support libraries for third-party systems.