public Widget asWidget() {
VerticalPanel content = new VerticalPanel();
content.setStyleName("fill-layout-width");
// table
RoleAssignmentKey keyProvider = new RoleAssignmentKey();
table = new DefaultCellTable<RoleAssignment>(5, keyProvider);
dataProvider = new ListDataProvider<RoleAssignment>(keyProvider);
dataProvider.addDataDisplay(table);
selectionModel = new SingleSelectionModel<RoleAssignment>(keyProvider);
table.setSelectionModel(selectionModel);