What logic are you using currently to set the value in "Interface::gUsersGroup"?
You're basically going to need to recreate that functionality for CWP. It might be easiest to create a simple accounts table that stores the user account name, and what group access they have, then add a quick find to set a session variable in PHP.
Once you've established that group as a variable, you'll want to add it to your query for the clients list that is returned.
Are you having users login to CWP with their own account credentials? Or did you hardcode your own CWP account credentials in?