removes remaining back office things from underlying UmbracoUserManager moves files

src/Umbraco.Infrastructure/Security/IdentityExtensions.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.AspNetCore.Identity;
+
+namespace Umbraco.Extensions
+{
+    public static class IdentityExtensions
+    {
+        public static string ToErrorMessage(this IEnumerable<IdentityError> errors)
+        {
+            if (errors == null) throw new ArgumentNullException(nameof(errors));
+            return string.Join(", ", errors.Select(x => x.Description).ToList());
+        }
+    }
+}