WBS-11 BFF Hardening: Implement auth caching state provider for instant sidebar transitions, forward proxy authentication cookies, and resolve WASM server-side prerendering BaseAddress null exception

src/dotnet/QuantEngine.Web/Pages/Account/Login.cshtml.cs

@@ -42,11 +42,22 @@ namespace QuantEngine.Web.Pages.Account
             try
             {
                 var loginRequest = new { Username = username, Password = password };
-                var requestUri = $"{Request.Scheme}://{Request.Host}/api/auth/login";
+                var scheme = string.IsNullOrWhiteSpace(Request.Scheme) ? "http" : Request.Scheme;
+                var host = Request.Host.HasValue ? Request.Host.Value : "localhost:5265";
+                var requestUri = $"{scheme}://{host}/api/auth/login";
                 var response = await _httpClient.PostAsJsonAsync(requestUri, loginRequest);
 
                 if (response.IsSuccessStatusCode)
                 {
+                    // Extract set-cookie header from API response and set it on proxy client response
+                    if (response.Headers.TryGetValues("Set-Cookie", out var cookieHeaders))
+                    {
+                        foreach (var cookieHeader in cookieHeaders)
+                        {
+                            Response.Headers.Append("Set-Cookie", cookieHeader);
+                        }
+                    }
+
                     if (rememberUsername)
                     {
                         Response.Cookies.Append(
@@ -84,5 +95,12 @@ namespace QuantEngine.Web.Pages.Account
                 return Page();
             }
         }
+
+        public IActionResult OnGetLogout()
+        {
+            // Revoke cookies securely
+            Response.Cookies.Delete("quant_auth_token");
+            return Redirect("/Account/Login");
+        }
     }
 }