C#

 string sUri = "http://ExchServer/Exchange/vonb/calendar/xxx"; //==>OK
//string sUri = "http://ExchServer/Exchange/vonb/calendar/xxx/yyy"; //==>Not OK even after the creation and 
//testing of the /xxx/ folder

	  
	        System.Uri myUri = new System.Uri(sUri);
	        HttpWebRequest HttpWRequest = (HttpWebRequest)WebRequest.Create(myUri);
	
	        string sQuery;
	        sQuery = "<?xml version='1.0'?>" + 
	          "<a:propertyupdate xmlns:a='DAV:' " + 
	          "xmlns:ex='http://schemas.microsoft.com/exchange/'>" + 
	          "<a:set><a:prop>" + 
	          "<ex:outlookfolderclass>IPF.Appointment</ex:outlookfolderclass>" + 
	          "</a:prop></a:set>" + 
	          "</a:propertyupdate>";
	
	        // Set Credentials
	        // TODO: Replace with appropriate user credentials
	        NetworkCredential myCred = new NetworkCredential(@"<myUser>", "<myPWD>");
	        CredentialCache myCredentialCache = new CredentialCache();
	        myCredentialCache.Add(myUri, "NTLM", myCred);
	        HttpWRequest.Credentials = myCredentialCache;
	
	        // Set Headers
	        HttpWRequest.KeepAlive = false; 
	        HttpWRequest.Headers.Set("Pragma", "no-cache");
	        HttpWRequest.ContentType =  "text/xml";
	        HttpWRequest.ContentLength = sQuery.Length;
	
	        //Set the request timeout to 5 minutes
	        HttpWRequest.Timeout = 300000;
	        // Set the request method
	        HttpWRequest.Method = "MKCOL";
	
	        // Store the data in a byte array
	        byte[] ByteQuery = System.Text.Encoding.ASCII.GetBytes(sQuery);
	        HttpWRequest.ContentLength = ByteQuery.Length;
	        Stream QueryStream = HttpWRequest.GetRequestStream();
	        // Write the data to be posted to the Request Stream
	        QueryStream.Write(ByteQuery,0,ByteQuery.Length);
	        QueryStream.Close();
	
	        // Send Request and Get Response
	        HttpWebResponse HttpWResponse = (HttpWebResponse)HttpWRequest.GetResponse();
	
	        // Get the Status code
	        int iStatCode =  (int)HttpWResponse.StatusCode;

WindowsIdentity identity = WindowsIdentity.GetCurrent();
WindowsPrincipal principal = new WindowsPrincipal(identity);

// Default provider is MyProvider
IAuthorizationProvider iAuthorizationProvider = AuthorizationFactory.GetAuthorizationProvider(); 
bool auth = iAuthorizationProvider.Authorize(principal, "BackUpAdmin");