If no action is specified in a request URL (for example, http://serverURL/grailsApp/someController), the plugin incorrectly assumes that the appropriate action for a redirect after login is the 'index' action. If the controller does not have an index action, this results in a 404 error. The CrowdAuthSecurityFilters.groovy should be using the defaultAction attribute of the controller class to ensure proper redirects in this situation. I've included a patch to correct the errant behaviour.