Add SecurityStampValidatorCallback to Identity module.

We don't use it, but sometimes it is useful.

modules/identity/src/Volo.Abp.Identity.AspNetCore/Volo/Abp/Identity/AspNetCore/AbpSecurityStampValidatorCallback.cs

@@ -0,0 +1,33 @@
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Identity;
+
+namespace Volo.Abp.Identity.AspNetCore
+{
+    public class AbpSecurityStampValidatorCallback
+    {
+        /// <summary>
+        /// Implements callback for SecurityStampValidator's OnRefreshingPrincipal event.
+        /// https://github.com/IdentityServer/IdentityServer4/blob/main/src/AspNetIdentity/src/SecurityStampValidatorCallback.cs
+        /// </summary>
+        public class SecurityStampValidatorCallback
+        {
+            /// <summary>
+            /// Maintains the claims captured at login time that are not being created by ASP.NET Identity.
+            /// This is needed to preserve claims such as idp, auth_time, amr.
+            /// </summary>
+            /// <param name="context">The context.</param>
+            /// <returns></returns>
+            public static Task UpdatePrincipal(SecurityStampRefreshingPrincipalContext context)
+            {
+                var newClaimTypes = context.NewPrincipal.Claims.Select(x => x.Type).ToArray();
+                var currentClaimsToKeep = context.CurrentPrincipal.Claims.Where(x => !newClaimTypes.Contains(x.Type)).ToArray();
+
+                var id = context.NewPrincipal.Identities.First();
+                id.AddClaims(currentClaimsToKeep);
+
+                return Task.CompletedTask;
+            }
+        }
+    }
+}