Thanks for this. You’re right that Kindle It currently works by making its own request for content, and thus fails to work on pages which are not publically accessible. We do have plans to offer an alternative method which will send the contents of the page you’re viewing to our servers for processing (currently it only sends the URL of the page to our servers, and then we fetch that URL).
I’m a little wary about how we go about implementing this. Some of the other read-later, send-to-kindle services work by sending the contents of the page you’re on to their own servers for processing. I’m not very fond of this approach because I can foresee many people invoking the service by mistake and having sensitive information immediately sent to someone else’s servers (for example, imagine clicking a button that did this while viewing your bank account statement - if you do this with out extension now, it will only send a URL which reveals very little, and fetching the URL will reveal no sensitive information). Of course in your case, and we’ve had requests from others who are in a similar situation, that’s exactly what you’d want. So I’m thinking about how best to integrate something like this.
One interim solution will be to offer a simple form where users can type/paste whatever they want to send to their Kindle. That would allow users to copy and paste content that’s currently protected into this form and make it accessible to our service, without necessarily making it accessible to the world.
In the meantime, I can only suggest that you try some of the other extensions similar to ours (e.g. Readability, Send to Kindle) which I think use the alternative approach of sending the contents of the page you’re on to their servers.
Hope that’s some help.