Update module 4 docs

Author: DamianEdwards

docs/4. Add auth features.md

@@ -456,6 +456,8 @@ In this module we're going to add the capability for users to register and sign-
 1. Add the following edit form to `EditSession.cshtml`:
 
    ```html
+    <h3>Edit Session</h3>
+
 	<form method="post" class="form-horizontal">
 	    <div asp-validation-summary="All" class="text-danger"></div>
 	    <input asp-for="Session.ID" type="hidden" />
@@ -496,7 +498,10 @@ In this module we're going to add the capability for users to register and sign-
 		</div>
 	    </div>
 	</form>
-	<partial name="_ValidationScriptsPartial" />
+    
+    @section Scripts {
+        <partial name="_ValidationScriptsPartial" />
+    }
    ```
 1. Add code to handle the `Save` and `Delete` button actions in `EditSession.cshtml.cs`:
 
@@ -590,6 +595,27 @@ on form posts:
    }
    ```
 
+> TempData-backed properties also flow across pages, so we can update the Index page to show the message value too, e.g. when the session is deleted
+
+1. Copy the message display markup from the top of the `EditSession.cshtml` file to the top of the `Index.cshtml` file:
+    ``` html
+    @if (Model.ShowMessage)
+    {
+        <div class="alert alert-success alert-dismissible" role="alert">
+            <button type="button" class="close" data-dismiss="alert" aria-label="Close"><span aria-hidden="true">&times;</span>   </button>
+            @Model.Message
+        </div>
+    }
+    ```
+1. Copy the properties from the `EditSession.cshtml.cs` Page Model class file to the `Index.cshtml.cs` Page Model too:
+    ``` csharp
+    [TempData]
+   public string Message { get; set; }
+
+   public bool ShowMessage => !string.IsNullOrEmpty(Message);
+    ```
+1. Rebuild and run the app then delete a session and observe it redirect to the home page and display the success message
+
 ## Create a Tag Helper for setting authorization requirements for UI elements
 We're currently using `if` blocks to determine whether to show parts of the UI based the user's auth policies. We can clean up this code by creating a custom [Tag Helper](https://docs.microsoft.com/en-us/aspnet/core/mvc/views/tag-helpers/intro).