public class BaseModule : IHttpModule
{
    private const double Treshold = 5;
    private string _filePath;

    public void Init(HttpApplication context)
    {
        _filePath = System.Web.Hosting.HostingEnvironment.MapPath("~/App_Data");

        context.PreRequestHandlerExecute += PreRequestHandler;
        context.PostRequestHandlerExecute += PostRequestHandler;
    }

    public void Dispose()
    {

    }

    protected void PreRequestHandler(object sender, EventArgs e)
    {
        var requestContext = ((HttpApplication)sender).Context;

        var timer = new Stopwatch();

        // Store timer in request
        requestContext.Items["Timer"] = timer;
        timer.Start();
    }

    protected void PostRequestHandler(object sender, EventArgs e)
    {
        var requestContext = ((HttpApplication)sender).Context;

        var timer = requestContext.Items["Timer"] as Stopwatch;
        if (timer == null)
            return;

        timer.Stop();

        var elapsedSeconds = timer.Elapsed.Seconds;
        if(elapsedSeconds > Treshold)
        {
            // Log slow running page
            File.AppendAllText(Path.Combine(_filePath, "slow-loading.txt"), GetWarning(requestContext, elapsedSeconds));
        }
    }

    protected string GetWarning(HttpContext context, double elapsedSeconds)
    {
        var sb = new StringBuilder();
        sb.AppendLine(string.Format("[{0}] [{1} seconds] ({2} {3}) ", DateTime.Now, elapsedSeconds, context.Request.HttpMethod, context.Request.Url));

        if(context.Request.HttpMethod == "POST")
        {
            for(var i = 0; i < context.Request.Form.Count; i++)
            {
                sb.AppendLine(string.Format("{0}: {1}", context.Request.Form.GetKey(i), context.Request.Form[i]));
            }
        }

        sb.AppendLine("-------------");
        return sb.ToString();
    }
}