Domain Specific Language with Fluent API

endpoint.cs

public static IFunctionFactory Factory { get; set; } = new FunctionFactory(new AppModule());

[FunctionName(nameof(XmlToXmlMapperHttpTrigger))]
public static async Task<HttpResponseMessage> Run(
    [HttpTrigger(AuthorizationLevel.Function, "post", Route = "mappers/xml/xml")] HttpRequestMessage req,
    ILogger log)
{
    return result = await Factory.Create<IXmlToXmlMapperFunction, ILogger>(log)
                                 .InvokeAsync<HttpRequestMessage, HttpResponseMessage>(req)
                                 .ConfigureAwait(false);
}

extension-method.cs

public static async Task<IXmlTransformHelper> AddArgumentsAsync(this Task<IXmlTransformHelper> helper, List<ExtensionObject> eos)
{
    var instance = await helper.ConfigureAwait(false);

    return await instance.AddArgumentsAsync(eos).ConfigureAwait(false);
}

function.cs

var content = await this._helper
                        .LoadXslAsync(this._settings.Containers.Mappers, request.Mapper.Directory, request.Mapper.Name)
                        .AddArgumentsAsync(request.ExtensionObjects)
                        .TransformAsync(request.InputXml);