Hi Suresh,
After Scaffolding Security, there should be a login.jsp in WebRoot/pages
You can modify this login page however you like. Or if you have a login page somewhere else, just update the security config in src/main/resources/[project]-generated-security-context.xml
To remove the Sitemesh decoration around the login page, add the following pattern to the excludes xml block in the WebRoot/WEB-INF/decorators.xml:
<pattern>/pages/login.jsp</pattern>
HTH,
Dave