Fix shopping cart, login, and register in FreshWingtipToys

Issue 1 - Shopping Cart: TextBox component was missing @onchange handler,
so TextChanged/OnTextChanged callbacks never fired. Added HandleChange
method to TextBox.razor.cs that updates Text, triggers validation, and
invokes both TextChanged and OnTextChanged callbacks. Wired @onchange
to both <input> and <textarea> elements in TextBox.razor.

Issue 2 - Login: SignInManager.PasswordSignInAsync cannot set cookies
from a SignalR circuit (InteractiveServer mode). Replaced direct
SignInManager call with navigation to a minimal API endpoint
(/Account/PerformLogin) that runs in HTTP context where cookies work.

Issue 3 - Register: Same SignalR cookie limitation. UserManager.CreateAsync
works fine in SignalR (no cookies), but SignInManager.SignInAsync does not.
After user creation, redirect to /Account/PerformRegisterSignIn endpoint
that validates credentials and sets the auth cookie via HTTP.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: csharpfritz

samples/FreshWingtipToys/Account/Login.razor.cs

@@ -1,40 +1,38 @@
 using Microsoft.AspNetCore.Components;
 using Microsoft.AspNetCore.Components.Web;
-using Microsoft.AspNetCore.Identity;
 
 namespace WingtipToys.Account
 {
     public partial class Login : ComponentBase
     {
-        [Inject] private SignInManager<IdentityUser> SignInManager { get; set; } = default!;
         [Inject] private NavigationManager Navigation { get; set; } = default!;
 
+        [SupplyParameterFromQuery(Name = "error")]
+        public string? ErrorParam { get; set; }
+
         private string email = "";
         private string password = "";
         private string errorMessage = "";
 
-        private async Task HandleLogin(MouseEventArgs args)
+        protected override void OnParametersSet()
+        {
+            if (!string.IsNullOrEmpty(ErrorParam))
+            {
+                errorMessage = ErrorParam;
+            }
+        }
+
+        private void HandleLogin(MouseEventArgs args)
         {
             if (string.IsNullOrWhiteSpace(email) || string.IsNullOrWhiteSpace(password))
             {
                 errorMessage = "Email and password are required.";
                 return;
             }
 
-            var result = await SignInManager.PasswordSignInAsync(email, password, isPersistent: false, lockoutOnFailure: false);
-
-            if (result.Succeeded)
-            {
-                Navigation.NavigateTo("/", forceLoad: true);
-            }
-            else if (result.IsLockedOut)
-            {
-                Navigation.NavigateTo("/Account/Lockout");
-            }
-            else
-            {
-                errorMessage = "Invalid login attempt.";
-            }
+            // Navigate to HTTP endpoint so SignInManager can set cookies via the HTTP response
+            var loginUrl = $"/Account/PerformLogin?email={Uri.EscapeDataString(email)}&password={Uri.EscapeDataString(password)}";
+            Navigation.NavigateTo(loginUrl, forceLoad: true);
         }
     }
 }

samples/FreshWingtipToys/Account/Register.razor.cs

@@ -7,7 +7,6 @@ namespace WingtipToys.Account
     public partial class Register : ComponentBase
     {
         [Inject] private UserManager<IdentityUser> UserManager { get; set; } = default!;
-        [Inject] private SignInManager<IdentityUser> SignInManager { get; set; } = default!;
         [Inject] private NavigationManager Navigation { get; set; } = default!;
 
         private string email = "";
@@ -34,8 +33,9 @@ private async Task HandleRegister(MouseEventArgs args)
 
             if (result.Succeeded)
             {
-                await SignInManager.SignInAsync(user, isPersistent: false);
-                Navigation.NavigateTo("/", forceLoad: true);
+                // Navigate to HTTP endpoint so SignInManager can set cookies via the HTTP response
+                var signInUrl = $"/Account/PerformRegisterSignIn?email={Uri.EscapeDataString(email)}&password={Uri.EscapeDataString(password)}";
+                Navigation.NavigateTo(signInUrl, forceLoad: true);
             }
             else
             {

samples/FreshWingtipToys/Program.cs

@@ -65,4 +65,37 @@
 app.MapRazorComponents<WingtipToys.Components.App>()
     .AddInteractiveServerRenderMode();
 
+// HTTP endpoint for login — SignInManager requires an active HTTP response to set cookies,
+// which is not available inside a SignalR circuit (InteractiveServer mode).
+app.MapGet("/Account/PerformLogin", async (
+    string email,
+    string password,
+    SignInManager<IdentityUser> signInManager) =>
+{
+    var result = await signInManager.PasswordSignInAsync(email, password,
+        isPersistent: false, lockoutOnFailure: false);
+
+    if (result.Succeeded)
+        return Results.Redirect("/");
+    if (result.IsLockedOut)
+        return Results.Redirect("/Account/Lockout");
+
+    return Results.Redirect("/Account/Login?error=" + Uri.EscapeDataString("Invalid login attempt."));
+});
+
+// HTTP endpoint for post-registration sign-in
+app.MapGet("/Account/PerformRegisterSignIn", async (
+    string email,
+    string password,
+    SignInManager<IdentityUser> signInManager) =>
+{
+    var result = await signInManager.PasswordSignInAsync(email, password,
+        isPersistent: false, lockoutOnFailure: false);
+
+    if (result.Succeeded)
+        return Results.Redirect("/");
+
+    return Results.Redirect("/Account/Login");
+});
+
 app.Run();

src/BlazorWebFormsComponents/TextBox.razor

@@ -4,10 +4,10 @@
 {
 	@if (TextMode == TextBoxMode.MultiLine)
 	{
-		<textarea @attributes="CalculatedAttributes">@Text</textarea>
+		<textarea @attributes="CalculatedAttributes" @onchange="HandleChange">@Text</textarea>
 	}
 	else
 	{
-		<input type="@CalculatedType" value="@Text" @attributes="CalculatedAttributes" />
+		<input type="@CalculatedType" value="@Text" @attributes="CalculatedAttributes" @onchange="HandleChange" />
 	}
 }

src/BlazorWebFormsComponents/TextBox.razor.cs

@@ -4,6 +4,7 @@
 using Microsoft.AspNetCore.Components;
 using System;
 using System.Collections.Generic;
+using System.Threading.Tasks;
 
 namespace BlazorWebFormsComponents
 {
@@ -71,6 +72,19 @@ public partial class TextBox : BaseStyledComponent, ITextComponent
 			_ => "text"
 		};
 
+		private async Task HandleChange(ChangeEventArgs e)
+		{
+			Text = e.Value?.ToString() ?? string.Empty;
+
+			if (CausesValidation && Coordinator != null)
+			{
+				Coordinator.ValidateGroup(ValidationGroup);
+			}
+
+			await TextChanged.InvokeAsync(Text);
+			await OnTextChanged.InvokeAsync(e);
+		}
+
 		internal Dictionary<string, object> CalculatedAttributes
 		{
 			get