"I`ll end up with 2 SecurityAssist Authenticate User Server Behaviors
which one should be used ?"
Both, One is used when the Login form is submitted, the other is used if the Auto Login option is checked.
In both of these SecurityAssist Authenticate User Server Behaviors, go to the Sessions tab, click the plus button and select the GroupsID Column to tore it's value in a session variable when the user logins in.
for details on creating User level authentication, see the User Level Authentication tutorial in the archived documentation section of the security assist support page:
it was written for V1, but the concept is still the same.