[FTP/FTPS Only] Begins an asynchronous request to supply the user-name to log into an account on the FTP server.
An IAsyncResult that references the asynchronous send.
You can create a callback method that implements the AsyncCallback delegate and pass its name to the BeginSendUserName method. The state argument may be used to pass in data that will be passed to the callback method.
For more information please refer to the synchronous version of this method, SendUserName.