Addendum to earlier posts:
I talked a little bit with the boss about the SSO limitations we've been discussing here in the forum, and that conversation changed the scope of the project a tad bit. In short, we do not really need a true SSO solution, as I had previously stated. What we need will just seem like SSO.
Ultimately, we need to have a user go to checkout and have the form data be pre-populated (e.g. address info, name, etc.). This means that I do not actually care if the user is registered within KonaKart or not; in fact, this seems to be the same as what KonaKart documentation refers to as 'one page checkout' (true? not true?). I do need to somehow pass the OpenCMS user data to the KonaKart checkout forms so that it can be used. This I'm not so sure how to do, though. Perhaps map values from the OpenCMS user object to a KonaKart customer object and then put that in the Session for use on the JSP by Struts?
Now, some of our products would require registration, and here's the solution I've come up with for that. Since I have direct control over the header and footer for all KonaKart pages, I could just insert some code into the header that would check for a token. That token would be placed there upon a user logging into our OpenCMS system. If the token was not present in the KonaKart header, the user would simply be redirected to a log-in page (or some such similar action).
With this solution in mind, I do see at least one caveat: how would our system (i.e. an OpenCMS eCommerce module) track orders placed by a user? If I understand KonaKart well enough, orders are stored using the email address as its identifying attribute, no? So if that's true, I should be able to retrieve all orders based on a user's email address.
Does this seem like a manageable workaround to accomplish my company's goals while continuing to stay within the bounds of the Community Edition? Am I breaking the future upgrade path for new versions of KonaKart by doing any of these things? And thank you for your help with these questions, @julie, it's very much appreciated!