When banning a user, a reason can be provided. The user will see this reason when trying to log in. Also log bans and unbans in the staff action logs.

app/assets/javascripts/admin/routes/admin_user_route.js

@@ -28,6 +28,13 @@ Discourse.AdminUserRoute = Discourse.Route.extend({
       controller.set('model', adminUser);
       window.scrollTo(0, 0);
     });
+  },
+
+  actions: {
+    showBanModal: function(user) {
+      Discourse.Route.showModal(this, 'admin_ban_user', user);
+      this.controllerFor('modal').set('modalClass', 'ban-user-modal');
+    }
   }
 
 });