v9: Remove install endpoint as valid endpoint (#11710)

* Remove installer endpoint from valid candidates

* Removed unrelevant change

src/Umbraco.Web.BackOffice/Install/InstallController.cs

@@ -13,6 +13,7 @@ using Umbraco.Cms.Core.Security;
 using Umbraco.Cms.Core.Services;
 using Umbraco.Cms.Core.WebAssets;
 using Umbraco.Cms.Infrastructure.Install;
+using Umbraco.Cms.Web.Common.Attributes;
 using Umbraco.Cms.Web.Common.Filters;
 using Umbraco.Extensions;
 
@@ -101,6 +102,7 @@ namespace Umbraco.Cms.Web.BackOffice.Install
         /// </summary>
         /// <returns></returns>
         [HttpGet]
+        [IgnoreFromNotFoundSelectorPolicy]
         public ActionResult Redirect()
         {
             var uri = HttpContext.Request.GetEncodedUrl();

src/Umbraco.Web.Common/Attributes/IgnoreFromNotFoundSelectorPolicyAttribute.cs

@@ -0,0 +1,13 @@
+using System;
+
+namespace Umbraco.Cms.Web.Common.Attributes
+{
+    /// <summary>
+    /// When applied to an api controller it will be routed to the /Umbraco/BackOffice prefix route so we can determine if it
+    /// is a back office route or not.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = true)]
+    public sealed class IgnoreFromNotFoundSelectorPolicyAttribute : Attribute
+    {
+    }
+}

src/Umbraco.Web.Website/Routing/NotFoundSelectorPolicy.cs

@@ -8,6 +8,7 @@ using Microsoft.AspNetCore.Mvc.Controllers;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.AspNetCore.Routing.Matching;
 using Umbraco.Cms.Core.Routing;
+using Umbraco.Cms.Web.Common.Attributes;
 using Umbraco.Cms.Web.Common.Controllers;
 using Umbraco.Cms.Web.Common.Routing;
 
@@ -80,11 +81,15 @@ namespace Umbraco.Cms.Web.Website.Routing
         {
             for (int i = 0; i < candidates.Count; i++)
             {
-                if (candidates.IsValidCandidate(i))
+                // We have to check if candidates needs to be ignored here
+                // So we dont return false when all endpoints are invalid
+                if (candidates.IsValidCandidate(i) &&
+                    candidates[i].Endpoint.Metadata.GetMetadata<IgnoreFromNotFoundSelectorPolicyAttribute>() is null)
                 {
                     return false;
                 }
             }
+
             return true;
         }
     }