public class TesteController: ApiController
{
    [HttpPost]
    public async Task<HttpResponseMessage> Upload()
    {
         return await FileUpload.Upload(Request);
    }
}


//Classe de upload.
public class FileUpload()
{
    public static async Task<HttpResponseMenssage> Upload(HttpRequestMessage request)
    {
         //processamento.
         return new HttpResponseMessage();
    }
}