User Profile

Hai, I need to authenticate the users at login with my own logic like, For eg: calling an external authentication server and using OpenDirectory in case if the server is not reachable.I know that i need to create an authorization plugin like the apple's sample code (NullAuthPlugin,NameAndPassword) and add an entry in authorizationdb at 'system.login.console' right to invoke my plugin to achieve this. NameAndPassword sample suggests to use different UI(using SFAuthorizationPluginView) other than the "loginwindow:login" to customize the login. Can I able to achieve my requirement without replacing the loginwindow GUI ie the mechanism "loginwindow:login"?? ie, Can i able to achieve this by keeping the existing mac's login screen as such and obtain the credentials to perform my own authentication ?? If possbile where should i place my mechanism at 'system.login.console' ?I think of replacing the <string>builtin:authenticate,privileged</string> with my own plugin to achieve my requirement ? Is it OK to replace the buitin login mechanism ?Is my approach correct ? Can anyone help me to clarify regarding this ?