How to show the auth page if the URL doesn't contain extra path?

I use Spring security plugin for our Grails application.

How to show the authentication page if the user typed the URL without any extra path, for example:

http://localhost:8080/OurGrail开发者_运维百科s

I use Config.groovy file to specify URL constraints:

grails.plugins.springsecurity.interceptUrlMap = [
    '/zoning/*': ['ROLE_USER'],
    '/**': ['IS_AUTHENTICATED_ANONYMOUSLY']
]

That would be '/': ['ROLE_USER'] and in some containers might also require '/index.gsp': ['ROLE_USER'].