The easier way as you said is OAM between both because both are totally integrated with the SSO solution of Oracle.
In case of Sites you have to replace the normal Login SSO process of CAS to be replaced by the OAM process.
As I know there aren't more approaches without developing custom classes to have Sites and Portal under the same SSO.
Thank you for your suggestions.
Can you point me to any resources which give more details of the implementations of your suggestions.
1.Replace the normal Login SSO process of CAS in Sites by the OAM process.
2.Develop custom classes to have Sites and Portal under the same SSO.
We have tried our some authentication cookie based approaches but could not get them to work.
It explains how to configure Sites to use the OAM classes in order to set the same Cookies \ Authentication process.
It should be enough to have Sites and Portal under the same SSO solution.
This really helps.