Yes, the recommended way to report broken links in the Grails documentation (including grails-spring-security-core) is to open a ticket (issue) in the relevant GitHub repository. This approach is confirmed by discussions in the Grails community, where users have reported broken documentation links by opening GitHub issues, and maintainers have responded and tracked the fixes through those tickets. For example, a user reported a broken documentation link for grails-spring-security-core, and the maintainers addressed it via GitHub issues and pull requests [Link to Documentation is Broken](
https://github.com/apache/grails-spring-security/issues/1096). So, for your case with the broken CAS link, you should open a new issue in the appropriate repository (e.g., apache/grails-spring-security) and provide details about the broken link. This helps the maintainers track and resolve documentation problems efficiently.