Fix #976: Break claims value in array into multiple claims (#996)

* Break claims value in array into multiple claims

* Review feedback 1

src/Microsoft.AspNetCore.Authentication.OpenIdConnect/OpenIdConnectHandler.cs

@@ -806,12 +806,7 @@ namespace Microsoft.AspNetCore.Authentication.OpenIdConnect
             }
 
             // adding remaining unique claims from userinfo endpoint to the identity
-            foreach (var pair in user)
+            ClaimsHelper.AddClaimsToIdentity(user, identity, jwt.Issuer);
-            {
-                JToken value;
-                var claimValue = user.TryGetValue(pair.Key, out value) ? value.ToString() : null;
-                identity.AddClaim(new Claim(pair.Key, claimValue, ClaimValueTypes.String, jwt.Issuer));
-            }
 
             return AuthenticateResult.Success(ticket);
         }

src/Microsoft.AspNetCore.Authentication.OpenIdConnect/Utility/ClaimsHelper.cs

@@ -0,0 +1,36 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Security.Claims;
+using Newtonsoft.Json.Linq;
+
+namespace Microsoft.AspNetCore.Authentication.OpenIdConnect
+{
+    internal static class ClaimsHelper
+    {
+        public static void AddClaimsToIdentity(
+            JObject userInformationPayload,
+            ClaimsIdentity identity,
+            string issuer)
+        {
+            foreach (var pair in userInformationPayload)
+            {
+                var array = pair.Value as JArray;
+                if (array != null)
+                {
+                    foreach (var item in array)
+                    {
+                        AddClaimsToIdentity(item, identity, pair.Key, issuer);
+                    }
+                }
+                else
+                {
+                    AddClaimsToIdentity(pair.Value, identity, pair.Key, issuer);
+                }
+            }
+        }
+
+        private static void AddClaimsToIdentity(JToken item, ClaimsIdentity identity, string key, string issuer)
+            => identity.AddClaim(new Claim(key, item?.ToString() ?? string.Empty, ClaimValueTypes.String, issuer));
+    }
+}