Allow strict mode while parsing JSON content type

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/AzureAppConfigurationOptions.cs

@@ -466,6 +466,15 @@ public AzureAppConfigurationOptions ConfigureStartupOptions(Action<StartupOption
             return this;
         }
 
+        /// <summary>
+        /// By default, the provider will throw a <see cref="FormatException"/> if a key-value with JSON content type has an invalid JSON value. This method silences the behavior and interprets the value as a string instead.
+        /// </summary>
+        public AzureAppConfigurationOptions DisableStrictJsonParsing()
+        {
+            JsonKeyValueAdapter.ThrowOnInvalidJson = false;
+            return this;
+        }
+
         private static ConfigurationClientOptions GetDefaultClientOptions()
         {
             var clientOptions = new ConfigurationClientOptions(ConfigurationClientOptions.ServiceVersion.V2023_10_01);

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/JsonKeyValueAdapter.cs

@@ -16,6 +16,8 @@ namespace Microsoft.Extensions.Configuration.AzureAppConfiguration
 {
     internal class JsonKeyValueAdapter : IKeyValueAdapter
     {
+        public static bool ThrowOnInvalidJson { get; set; } = true;
+
         private static readonly IEnumerable<string> ExcludedJsonContentTypes = new[]
         {
             FeatureManagementConstants.ContentType,
@@ -42,7 +44,13 @@ public Task<IEnumerable<KeyValuePair<string, string>>> ProcessKeyValue(Configura
             }
             catch (JsonException)
             {
-                // If the value is not a valid JSON, treat it like regular string value
+                if (ThrowOnInvalidJson)
+                {
+                    throw new FormatException($"Invalid JSON value for key '{setting.Key}' with content type '{setting.ContentType}'. Please ensure the value is properly formatted JSON.");
+                }
+
+                logger.LogWarning($"Invalid JSON value for key '{setting.Key}' with content type '{setting.ContentType}'. Treated as a string value.");
+
                 return Task.FromResult<IEnumerable<KeyValuePair<string, string>>>(new[] { new KeyValuePair<string, string>(setting.Key, setting.Value) });
             }
 

tests/Tests.AzureAppConfiguration/JsonContentTypeTests.cs

@@ -124,6 +124,49 @@ public void JsonContentTypeTests_LoadSettingsWithInvalidJsonContentTypeAsString(
             Assert.Equal("{}", config["TestKey7"]);
         }
 
+        [Fact]
+        public void JsonContentTypeTests_StrictJsonParsingEnabled()
+        {
+            List<ConfigurationSetting> _kvCollection = new List<ConfigurationSetting>
+            {
+                ConfigurationModelFactory.ConfigurationSetting(
+                    key: "TestKey1",
+                    value: "}{",
+                    contentType: "application/json")
+            };
+            var mockClientManager = GetMockConfigurationClientManager(_kvCollection);
+
+            var builder = new ConfigurationBuilder()
+                .AddAzureAppConfiguration(options => 
+                {
+                    options.ClientManager = mockClientManager;
+                });
+
+             Assert.Throws<FormatException>(() => builder.Build());
+        }
+
+        [Fact]
+        public void JsonContentTypeTests_StrictJsonParsingDisabled()
+        {
+            List<ConfigurationSetting> _kvCollection = new List<ConfigurationSetting>
+            {
+                ConfigurationModelFactory.ConfigurationSetting(
+                    key: "TestKey1",
+                    value: "}{",
+                    contentType: "application/json")
+            };
+            var mockClientManager = GetMockConfigurationClientManager(_kvCollection);
+
+            var builder = new ConfigurationBuilder()
+                .AddAzureAppConfiguration(options =>
+                {
+                    options.ClientManager = mockClientManager;
+                    options.DisableStrictJsonParsing();
+                });
+
+            Assert.NotNull(builder.Build());
+        }
+
         [Fact]
         public void JsonContentTypeTests_OverwriteValuesForDuplicateKeysAfterFlatteningJson()
         {