Updated the code as per the requirements of the exercise.
Could not complete the exercise as expected due to following reasons:
1. The base version of application provided in exercise did not run and had several issues which consumed some time to be fixed.
2. I have not had an opportunity to work with Grails for more than a year so I was out of shape as regards to Grails.
3. I didn't have an opportunity to setup Spring Security Plugin with Grails before, so it took up almost all the time, still getting some issues in adding users into database.
4. Given more time I would have been able to finish the entire exercise properly.