OIDC offline session refresh has no access to previous session info

For a custom plugin, I need to access the _samlToken stored at login time in getUser.

Currently, the offline refresh code does not allow it:

        $req->user( $refreshSession->data->{_session_uid} );
        $req->data->{$_} = $refreshSession->data->{$_} foreach (qw(_choice));
        $req->steps( [
                'getUser',        @{ $self->p->betweenAuthAndData },
                'setSessionInfo', $self->p->groupsAndMacros,
                'setLocalGroups',
            ]
        );

Only _choice is kept, and the _samlToken cannot be exposed to getUser

In order to fix this, a possible solution would be to run the same process we do in the "Refresh my rights" feature: keep existing session keys, refresh, and update the session with the new keys. This will remove some code duplication between OIDC and Main