add cache-control header to prevent checkout pages from being cached.

Author: umbracotrd

src/Umbraco.Commerce.Checkout/Web/Controllers/Filters/NoStoreCacheControlAttribute.cs

@@ -0,0 +1,15 @@
+using Microsoft.AspNetCore.Mvc.Filters;
+
+namespace Umbraco.Commerce.Checkout.Web.Controllers.Filters
+{
+    /// <summary>
+    /// Add "cache-control: no-store" header to the response.
+    /// </summary>
+    internal sealed class NoStoreCacheControlAttribute : ActionFilterAttribute
+    {
+        public override void OnActionExecuted(ActionExecutedContext context)
+        {
+            context.HttpContext.Response.Headers.CacheControl = "no-store";
+        }
+    }
+}

src/Umbraco.Commerce.Checkout/Web/Controllers/UmbracoCommerceCheckoutBaseController.cs

@@ -8,9 +8,11 @@
 using Umbraco.Commerce.Core.Api;
 using Umbraco.Commerce.Core.Models;
 using Umbraco.Extensions;
+using Umbraco.Commerce.Checkout.Web.Controllers.Filters;
 
 namespace Umbraco.Commerce.Checkout.Web.Controllers
 {
+    [NoStoreCacheControl]
     public abstract class UmbracoCommerceCheckoutBaseController : RenderController
     {
         protected UmbracoCommerceCheckoutBaseController(