You can use GeoServer's virtual service endpoints to do this. For example, if your normal WMS endpoint is http://localhost:8080/geoserver/wms , you can use http://localhost:8080/geoserver/A/wms for just the layers in the A workspace.
You can also use http://localhost:8080/geoserver/A/people/wms for just the single A:people layer.
This isn't totally secure though, so if you are worried about any access of other layers, you should set up some security rules.