At present, we only support the Pega API REST service calls on the default application. Of course your own REST services can take an access group or application parameter and switch as necessary. Assuming you are invoking the Pega APIs, this means that App A must be the default access group. So, if you want a browser-connected user to auto-switch to App B on login, you can call RedirectAndRun from the "Starting activity to execute" on the operator ID. Let me know if you run into problems with this approach.