Add IComponent validation and improve documentation for NotAuthorizedPage

Co-authored-by: javiercn <6995051+javiercn@users.noreply.github.com>

Author: Copilot

src/Components/Authorization/src/AuthorizeRouteView.cs

@@ -53,7 +53,7 @@ public AuthorizeRouteView()
 
     /// <summary>
     /// The page type that will be displayed if the user is not authorized.
-    /// The page type must implement <see cref="IComponent"/> and have a <see cref="RouteAttribute"/>.
+    /// The page type must implement <see cref="IComponent"/>.
     /// </summary>
     [Parameter]
     [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
@@ -121,6 +121,12 @@ private void RenderNotAuthorizedInDefaultLayout(RenderTreeBuilder builder, Authe
     {
         if (NotAuthorizedPage is not null)
         {
+            if (!typeof(IComponent).IsAssignableFrom(NotAuthorizedPage))
+            {
+                throw new InvalidOperationException($"The type {NotAuthorizedPage.FullName} " +
+                    $"does not implement {typeof(IComponent).FullName}.");
+            }
+
             RenderPageInDefaultLayout(builder, NotAuthorizedPage);
         }
         else

src/Components/Authorization/test/AuthorizeRouteViewTest.cs

@@ -434,6 +434,28 @@ public void WhenNotAuthorized_NotAuthorizedPageTakesPriorityOverNotAuthorizedCon
             edit => AssertPrependText(batch, edit, "Layout ends here"));
     }
 
+    [Fact]
+    public void WhenNotAuthorized_ThrowsForInvalidNotAuthorizedPageType()
+    {
+        // Arrange: set NotAuthorizedPage to a type that doesn't implement IComponent
+        var routeData = new RouteData(typeof(TestPageRequiringAuthorization), EmptyParametersDictionary);
+        _testAuthorizationService.NextResult = AuthorizationResult.Failed();
+
+        // Act & Assert
+        var exception = Assert.Throws<InvalidOperationException>(() =>
+        {
+            _renderer.RenderRootComponent(_authorizeRouteViewComponentId, ParameterView.FromDictionary(new Dictionary<string, object>
+            {
+                { nameof(AuthorizeRouteView.RouteData), routeData },
+                { nameof(AuthorizeRouteView.DefaultLayout), typeof(TestLayout) },
+                { nameof(AuthorizeRouteView.NotAuthorizedPage), typeof(string) }, // string doesn't implement IComponent
+            }));
+        });
+
+        Assert.Contains("does not implement", exception.Message);
+        Assert.Contains("IComponent", exception.Message);
+    }
+
     private static void AssertPrependText(CapturedBatch batch, RenderTreeEdit edit, string text)
     {
         Assert.Equal(RenderTreeEditType.PrependFrame, edit.Type);