Added section to describe how parts of the UI can be hidden based on user role

advanced/fiori.md

@@ -485,6 +485,47 @@ SELECT.from(Books.drafts) //returns all drafts of the Books entity
 
 [Learn how to query drafts in Java.](../java/fiori-drafts#draftservices){.learn-more}
 
+## Use user roles to toggle visibility of UI elements
+
+In some use cases you might want to hide parts of the UI for specific users. This is possible by using the respective UI annotations like `@UI.Hidden` or `@UI.CreateHidden` in conjunction with '$edmJson' pointing to a singleton.
+
+First you would define the [singleton](../advanced/odata#singletons) in your service and annotate it also with ['@cds.persistency.skip'](../guides/databases#cds-persistence-skip) so that no database artefact is created.
+
+```cds
+    @odata.singleton @cds.persistency.skip
+    entity Configuration {
+        key ID: String; //A key is technically not required as it is a singleton, however without it some consumers might run into problems
+        isAdmin : Boolean;
+    }
+```
+
+Secondly define an on handler for serving the request
+
+```js
+srv.on('READ', 'Configuration', async req => {
+    req.reply({
+        isAdmin: req.user.is('admin') //admin is the role, which for example is also used in @requires annotation
+    });
+});
+```
+
+and thirdly refer to the singleton in the annotation by using a [dynamic expression](../advanced/odata#dynamic-expressions)
+
+```cds
+annotate service.Books with @(
+    UI.CreateHidden : { $edmJson: {$Not: { $Path: '/CatalogService.EntityContainer/Configuration/isAdmin'} } },
+    UI.UpdateHidden : { $edmJson: {$Not: { $Path: '/CatalogService.EntityContainer/Configuration/isAdmin'} } },
+);
+```
+
+The Entity Container is OData specific and refers to the '$metadata' of the OData service in which all accessible entities are located within the Entity Container. SAP Fiori elements also allows to not include it in the path:
+
+```cds
+annotate service.Books with @(
+    UI.CreateHidden : { $edmJson: {$Not: { $Path: '/Configuration/isAdmin'} } },
+    UI.UpdateHidden : { $edmJson: {$Not: { $Path: '/Configuration/isAdmin'} } },
+);
+```
 
 ## Value Helps