Ensuring json keys are lowercase in .NET

protected void Application_Start() {
    JsonConfig.Configure();   
}

public static class JsonConfig
{
    public static void Configure(){
        var formatters = GlobalConfiguration.Configuration.Formatters;
        var jsonFormatter = formatters.JsonFormatter;
        var settings = jsonFormatter.SerializerSettings;

        settings.ContractResolver = new CamelCasePropertyNamesContractResolver();
    }
}

You can create a custom contract resolver for this. The following contract resolver will convert all keys to lowercase:

public class LowercaseContractResolver : DefaultContractResolver
{
    protected override string ResolvePropertyName(string propertyName)
    {
        return propertyName.ToLower();
    }
}

Usage:

var settings = new JsonSerializerSettings();
settings.ContractResolver = new LowercaseContractResolver();
var json = JsonConvert.SerializeObject(authority, Formatting.Indented, settings);

Wil result in:

{"username":"Mark","apitoken":"xyzABC1234"}

---

If you always want to serialize using the LowercaseContractResolver, consider wrapping it in a class to avoid repeating yourself:

public class LowercaseJsonSerializer
{
    private static readonly JsonSerializerSettings Settings = new JsonSerializerSettings
    {
        ContractResolver = new LowercaseContractResolver()
    };

    public static string SerializeObject(object o)
    {
        return JsonConvert.SerializeObject(o, Formatting.Indented, Settings);
    }

    public class LowercaseContractResolver : DefaultContractResolver
    {
        protected override string ResolvePropertyName(string propertyName)
        {
            return propertyName.ToLower();
        }
    }
}

Which can be used like this:

var json = LowercaseJsonSerializer.SerializeObject(new { Foo = "bar" });
// { "foo": "bar" }

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ASP.NET MVC4 / WebAPI

If you are using ASP.NET MVC4 / WebAPI, you can use a CamelCasePropertyNamesContractResolver from Newtonsoft.Json library which included by default.