ExceptionLogger

    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {

            // Web API routes
            config.MapHttpAttributeRoutes();

            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );

            //error log
            GlobalConfiguration.Configuration.IncludeErrorDetailPolicy = IncludeErrorDetailPolicy.Always;
            config.Services.Add(typeof(IExceptionLogger), new ApiExceptionLogger());
        }
    }

       protected void Application_Error(object sender, EventArgs e)
        {
            Response.Filter = null;
            var lastError = Server.GetLastError();
            if (lastError != null)
            {
                _logger.Error(lastError, "CRM site exception");
            }
        }    

    public class ApiExceptionLogger: ExceptionLogger
    {
        public ApiExceptionLogger(){}

        public override void Log(ExceptionLoggerContext context)
        {
            StringBuilder sb = new StringBuilder();
            var r = context.Request;
            if (r != null)
            {
                sb.AppendLine($"Unhandled exception processing {r.Method} for {r.RequestUri}");
                if (r.Headers.Count() > 0)
                {
                    sb.AppendLine("Headers Begin:");
                    sb.AppendLine($"{r.Headers.ToString()}");
                    sb.AppendLine("Headers End.");
                }
                if (r.Content!=null)
                {
                    var content = r.Content.ReadAsStringAsync().Result;
                    sb.AppendLine("Contents Begin:");
                    sb.AppendLine(content);
                    sb.AppendLine("Contents End.");
                }
            }
            IIocHelper ioc = IocFactory.Instance;
            var logger = ioc.GetInstance<ILogBase>();
            logger.Error(sb.ToString(), context.Exception);
        }

    }