[Bug]: Enum dictionary keys not supported by the default Refit settings, CamelCaseStringEnumConverter throws an exception

[Kloizdena]

Describe the bug 🐞

When I try to send or receive a dictionary with an enum key with the default Refit settings, it throws an exception because the JsonSerializer added to the default Refit settings does not override the ReadAsPropertyName and WriteAsPropertyName methods.

Step to reproduce

Run the following code as a Console app:

using System.Text.Json;

var jsonOptions = Refit.SystemTextJsonContentSerializer.GetDefaultJsonSerializerOptions();
var dictionary = new Dictionary<MyEnum, string>
{
    [MyEnum.FirstValue] = "a",
    [MyEnum.SecondValue] = "b",
};
// Fails with StackOverflowException
_ = JsonSerializer.Serialize(dictionary, jsonOptions);

// Fails with System.NotSupportedException:
// 'The type 'System.Object' is not a supported dictionary key using converter of type 'System.Text.Json.Serialization.Converters.DefaultObjectConverter'.
// Custom converters can add support for dictionary key serialization by overriding the 'ReadAsPropertyName' and 'WriteAsPropertyName' methods.
_ = JsonSerializer.Deserialize<Dictionary<MyEnum, string>>(@"{""FirstValue"": ""a""}", jsonOptions);

public enum MyEnum
{
    FirstValue,
    SecondValue,
}

csproj:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net9.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>
	<ItemGroup>
		<PackageReference Include="Refit" Version="10.1.6" />
	</ItemGroup>
</Project>

Reproduction repository

https://github.com/reactiveui/refit

Expected behavior

The enum converter should support serializing enums as dictionary keys

Screenshots 🖼️

No response

IDE

No response

Operating system

No response

Version

No response

Device

No response

Refit Version

10.1.6

Additional information ℹ️

No response

[glennawatson]

Additional detail from #2134 (closed as duplicate), including a regression range:

• Regression appears after upgrading from 10.0.1 to 10.1.x and persists in 11.x.
• Symptom: deserializing a response containing a Dictionary<TEnum, ...> (enum used as a dictionary key) throws "System.NotSupportedException: The type 'System.Object' is not a supported dictionary key".
• Root cause: the default CamelCaseStringEnumConverter is a typed JsonConverter<object?> that does not override ReadAsPropertyName / WriteAsPropertyName. When an enum is used as a dictionary key, System.Text.Json routes the key through this converter, and without the AsPropertyName overrides it falls back to the object-key path and throws.
• Likely fix: implement ReadAsPropertyName/WriteAsPropertyName on the converter, or defer to the built-in JsonStringEnumConverter for key handling.