Dear guys
Now I could get a token in endpoint page.
My code described below

Yahoo.Authentication auth = new Yahoo.Authentication(AppID, Secret);
auth.Token = token;
auth.UpdateCredentials();

ymws ymwsInstance = new ymws();
ymwsInstance.Url =
String.Concat("http://mail.yahooapis.com/ws/mail/v1.1/soap?appid=",
auth.ApplicationId, "&wssid=", auth.WssId);
ymwsInstance.CookieContainer = new CookieContainer();
ymwsInstance.CookieContainer.Add(new
Uri("http://mail.yahooapis.com/"), new Cookie("Y",
auth.Cookies.Trim().Substring(2)));
try {
GetUserDataResponse userData = ymwsInstance.GetUserData(new
GetUserData());
}catch (Exception ex) {
Response.Write(ex.Message);
}

but ymwsInstance.GetUserData got an error, I just can see the message
is Not allowed but without other hint, and the StackTrack list below

System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMess\
age
message, WebResponse response, Stream responseStream, Boolean asyncCall)
System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String
methodName, Object[] parameters)
com.yahooapis.mail.ymws.GetUserData(GetUserData GetUserData1) at
c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET
Files\root\26676eb7\92c7e946\App_WebReferences.rofz3kg8.0.cs: Line 159
_Default.Page_Load(Object sender, EventArgs e) at
c:\Inetpub\wwwroot\Default.aspx.cs: Line 76
is there anyone could be kind enough to tell me how to solve this?
thanks wholeheartedly