update news

NEWS.md

@@ -3,6 +3,7 @@
 - Documentation update only:
   - Clarify that you can use `get_managed_token` to obtain tokens with a user-defined identity, not just a system identity
   - Clarify the distinction between authentication and authorization in the `get_azure_token` help, and also in the Shiny vignette
+  - Add a webapp (Shiny) scenario to the "Common authentication scenarios" vignette
 
 # AzureAuth 1.3.2