If Tableau Server only trusts your web server, then it doesn't trust your dev server. Therefore, requests for a ticket from the dev machine will fail - because we don't trust it. That's how trusted authentication is supposed to work.
Either request your tickets by way of the web server (which is trusted), or make your dev machine trusted, too. You can do your testing / development, then remove it from the list of trusted machines when you go live.
Hope this helps!
Thanks for the reply. I am clear about trusted authentication now. I made it working by running a web service on Web server which generate ticket and call that web service from my dev machine as you suggested.
That is the best approach. You can then open up the web service to your external customers when the time comes.