阻止对asp.net .asmx Web服务的跨域调用

public class CORSAttribute : System.Attribute, System.Web.Services.Protocols.SoapHeaderAttribute
{
    public override void ProcessMessage(System.Web.Services.Protocols.SoapMessage message)
    {
        HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin", "*");
        HttpContext.Current.Response.AddHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, PUT, DELETE");
        HttpContext.Current.Response.AddHeader("Access-Control-Allow-Headers", "Content-Type, Accept, Authorization");
    }
}

[WebMethod]
[CORS]
public string MyWebMethod()
{
    return "Hello, world!";
}

[WebMethod]
[ScriptMethod(ResponseFormat = ResponseFormat.Json)]
public string MyWebMethod(string callback)
{
    string result = "Hello, world!";

    if (!string.IsNullOrEmpty(callback))
    {
        result = callback + "(" + result + ");";
    }

    return result;
}

function myCallback(data) {
    alert(data);
}

var script = document.createElement('script');
script.src = 'http://example.com/MyWebService.asmx/MyWebMethod?callback=myCallback';
document.body.appendChild(script);