Post Password Redirect

I want to be able to give clients promo codes. When they visit the website and input the promo code it will direct them to the password protected post.

To hide the password protected posts I’ll be using Alphawolf’s Admin Management Xtended plugin. To destroy the post password cookie I’ll be using the “Simple WordPress Hack: Delete “wp_postpass” Cookie” from http://michaelpark.net.

I’ll be using a logic to check if the supplied promo code is equal post_password in the database. If the post_password is correct it will redirect the user via wp_redirect() based on the guid to the correct page.

The problem I have, is how do I create the post password cookie so that the user doesn’t have to input the password again to view the post.

If there is already a plugin for this I’d appreciate where to locate it. Also please let me know if I’m on the right track.