Handle `null`s in the `JsonDocumentAuthExtensions.GetString` extension method (#10252)

src/Security/Authentication/Core/src/JsonDocumentAuthExtensions.cs

@@ -7,8 +7,14 @@ namespace Microsoft.AspNetCore.Authentication
 {
     public static class JsonDocumentAuthExtensions
     {
-        public static string GetString(this JsonElement element, string key) =>
-            element.TryGetProperty(key, out var property)
-                ? property.ToString() : null;
+        public static string GetString(this JsonElement element, string key)
+        {
+            if (element.TryGetProperty(key, out var property) && property.Type != JsonValueType.Null)
+            {
+                return property.ToString();
+            }
+
+            return null;
+        }
     }
 }

src/Security/Authentication/MicrosoftAccount/src/MicrosoftAccountOptions.cs

@@ -27,15 +27,7 @@ namespace Microsoft.AspNetCore.Authentication.MicrosoftAccount
             ClaimActions.MapJsonKey(ClaimTypes.Name, "displayName");
             ClaimActions.MapJsonKey(ClaimTypes.GivenName, "givenName");
             ClaimActions.MapJsonKey(ClaimTypes.Surname, "surname");
-            ClaimActions.MapCustomJson(ClaimTypes.Email, user =>
-            {
-                var mail = user.GetString("mail");
-                if (string.IsNullOrEmpty(mail))
-                {
-                    mail = user.GetString("userPrincipalName");
-                }
-                return mail;
-            });
+            ClaimActions.MapCustomJson(ClaimTypes.Email, user => user.GetString("mail") ?? user.GetString("userPrincipalName"));
         }
     }
 }

src/Security/Authentication/test/JsonDocumentAuthExtensionsTests.cs

@@ -0,0 +1,26 @@
+// 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.Text.Json;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Authentication.Test
+{
+    public class JsonDocumentAuthExtensionsTests
+    {
+        [Theory]
+        [InlineData("{ \"foo\": null }", null)]
+        [InlineData("{ \"foo\": \"\" }", "")]
+        [InlineData("{ \"foo\": \"bar\" }", "bar")]
+        [InlineData("{ \"foo\": 1 }", "1")]
+        [InlineData("{ \"bar\": \"baz\" }", null)]
+        public void GetStringReturnsCorrectValue(string json, string expected)
+        {
+            using (var document = JsonDocument.Parse(json))
+            {
+                var value = document.RootElement.GetString("foo");
+                Assert.Equal(expected, value);
+            }
+        }
+    }
+}

src/Security/Authentication/test/MicrosoftAccountTests.cs

@@ -203,8 +203,7 @@ namespace Microsoft.AspNetCore.Authentication.Tests.MicrosoftAccount
                                 displayName = "Test Name",
                                 givenName = "Test Given Name",
                                 surname = "Test Family Name",
-                                mail = "",
-                                userPrincipalName = "Test email"
+                                mail = "Test email"
                             });
                         }