You will then be able to enter the podcast RSS feed url. You will have to check the 'Authentication' checkbox and enter your login / password.
After validation the app will update the podast. You can change the login/password at any time by long rpessing on the podcast, then selecting 'Custom Settings' and finally 'Edit podcast url'.
For older versions:
In order to subscribe to an authenticated feed, you will have to use the following RSS feed pattern:
where 'the_rss_feed_url' is your podcast RSS feed url WITHOUT the 'http://' prefix