Hello Hao,

The two-request behavior you saw is due to the authentication process of
windows intergated authentication, and this is a transport layer
authentication behavior rather than webservice code specific behavior.  
When performing windows authentication, the client browser will send
request without authentication credential info, and if server-side require
user authentication, it deny the access and then a second request goes.  So
far, one means for improve such authentication peformance is to se the
"PreAuthenticate" header of http request(webservice client proxy has a
property for this), however, only limited authentication scheme support
this "PreAuthenticate" setting. here is a webarticle which has mentioned
this:

#Web Service optimization
http://www.codeproject.com/soap/webserviceoptimization.asp

You can have a look to get more idea.

Hope this helps.

Sincerely,

Steven Cheng

Microsoft MSDN Online Support Lead



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This posting is provided "AS IS" with no warranties, and confers no rights.

Don't bother with PreAuthenticate. To make this work properly you will have
to override the GetWebRequest method in your client proxy.

Add something like this to your code (change "YourReference" to the name of
your Web Reference):

 class OBACnetWSCore : YourReference.BACnetWSCore {
   protected override WebRequest GetWebRequest(Uri uri) {
     HttpWebRequest webRequest = (HttpWebRequest)base.GetWebRequest(uri);
     NetworkCredential creds = Credentials as NetworkCredential;
     if (creds != null) {
       string authStr =
         ((creds.Domain != null) && (creds.Domain.Length > 0) ?
           creds.Domain + @"\" : string.Empty) +
         creds.UserName + ":" + creds.Password;
       authStr = Convert.ToBase64String(Encoding.Default.GetBytes(authStr));
       webRequest.Headers["Authorization"] = "Basic " + authStr;
     }
     return webRequest;
   }
 }

...and then use OBACnetWSCore for your proxy.

/Hans