[keycloak-user] info about sso without login prompt

Dear all, I'm using keycloak js adapter in order to log in user into an application. I need to integrate a previous system of authentication with this new one. To do this, I use user's credentials passed by the old system, to automatically retrieve keycloak grant calling the related web service. So I have the session data but I'm not able to use single-sign-on in fact when I open another tab the user isn't logged in anymore. I need to know if there is a way to create a sso session, if I must use cookies or browser local storage. Thank you for your time Sincerely, Marianna Notarnicola