Hi VarunGrazitti ,
In case of SSO, login and registration pages are usually not hosted on Lithium side but live on the identity provider side (the user is redirected to an external site where he logs in). Therefore the out-of-the-box modal dialogs we have for Lithium login/registration are not applicable for SSO.
In case of a custom SSO solution, you could build your own login page with a custom component that uses a modal dialog - see here. This would however require your custom component to have the code for user authentication.
Hope this helps!