I have tried that tutorial, and it’s now outdated due to the Okta Grails plugin no longer being available. The bintray repository where the Okta Grails plugin was hosted, has been shut down. Trying that project, the build fails because of that Okta dependency, since the repository no longer exists.
Without it, another way has to be implemented to use Okta.
It will be nice to have that update, ideally for people like me working on legacy applications using Grails as the back-end. Most of the applications I work with are in Grails 2.x to Grails 3.x. I hope the Okta team will also think about us.