Hi Sudheer,
when using an IDP, you must have a user account AEM. Either created before or auto created on login. If you wish to extend the authentication handler you could create a generic user that all your users get mapped to. After login, you would then call a backend system (e.g. CRM) and get the users profile details, this data would then be stored in the client browser[1] and loaded into the client context/ContextHub you could then do personalization.
You need to consider if you want to create a user in AEM and if the users profile data should be stored in AEM, often companies will have their own form of CRM that they store all their customers details, so it makes sense not to duplicate this data by storing it again in AEM.
Regards,
Opkar
[1] https://docs.adobe.com/docs/en/aem/6-1/develop/personalization/contexthub/ch-extend.html#par_title_2...