Merge pull request #2707 from KoenZomers/AcsConnectToNonExistantSiteError

Added clearer feedback when using ACS to connect to a site that does not exist

Author: gautamdsheth

src/Commands/Base/PnPConnection.cs

@@ -196,6 +196,11 @@ internal static PnPConnection CreateWithACSAppOnly(Uri url, string realm, string
                     if (realm == null)
                     {
                         realm = GetRealmFromTargetUrl(url);
+
+                        if(realm == null)
+                        {
+                            throw new Exception($"Could not determine realm for the target site '{url}'. Please validate that a site exists at this URL.");
+                        }
                     }
 
                     if (url.DnsSafeHost.Contains("spoppe.com"))
@@ -772,7 +777,7 @@ internal static string GetRealmFromTargetUrl(Uri targetApplicationUri)
             client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", "");
 
             var response = client.GetAsync(targetApplicationUri + "/_vti_bin/client.svc").GetAwaiter().GetResult();
-            if (response == null)
+            if (response == null || response.StatusCode == System.Net.HttpStatusCode.NotFound)
             {
                 return null;
             }