Chrome Store payment auth implementation - PHP

We have recently released a hosted app on the chrome web store & we need someone to implement oauth on the PHP page that hosts the app. Here is a page explaining how it should go: [login to view URL] We implemented an [login to view URL] file & a [login to view URL] file that google provided but could not get the example to work. In the dev dashboard, there is a link to oauth setup where you can request the token & secret, but the secret field is blank. We could provide server access to the hosted app as well as dev dashboard access. We are looking for someone familiar/experienced with OAuth Setup on a hosted app in the Chrome Web Store to implement the OAuth check on the php page to determine if users have purchased the app. The example we initially tried to implement can be used, or a different working solution is welcome as well. We would like to defer to the developer on what method is going to be most efficient and effective and are looking for suggestions.