Restricting access to a webservice in ASP.NET

Restricting access to a webservice can be done via web.config but if you would want to make the decision at runtime then here is an example of how you could achieve this

 

protected void Application_BeginRequest(Object sender, EventArgs e)
{
  if (/*Condition*/)
  {
    if (HttpContext.Current.Request.Url.ToString().Contains("Admin.asmx"))
    {
       HttpContext.Current.Response.StatusCode = 404;
    }
   }
}

Genius ain't anything more than elegant common sense.
Josh Billings