SSO Kit: Document how to integrate external roles

[tarekoraby]

Vote to prioritize: add a 👍 reaction to help the community and maintainers prioritize this issue.

Tell us about your request

The SSO Kit's documentation should highlight how to integrate roles that are retrieved from an external source (e.g., a database) to implement access control for Flow views. @heruan advised that this could be done by implementing UserDetailsService, but the documentation should provide an example of how to do that.