Looking for e-commerce plugin to sell access

I’m evaluating whether WordPress is a good enough backbone to our e-commerce need. We want to sell access to apps through a subscription (monthly) model with a store front end – probably paypal based, but I’m open to others if they work well with australian tax stuff.

The apps are not pages within wordpress directly – so it’s not really a “member plugin” type arrangement as far as I can tell, rather the external app sites would be able to query WordPress in order to verify a users current subscription.

So products are neither physical, or file downloads. They are authentication itself, sold through a payment gateway. A users “download” link is actually therefore a single-sign on token to an area in a third-party web site.

Products are added like normal e-commerce products however, and have coupons & discounts, ratings, review pages, slideshows, just like normal products. I’ve been trying to coax information out of many commercial shop services but everyone seems geared towards either physical products, or digital downloads – and we have neither.

Can anyone suggest a product? I’m pretty sure I’ll have to customise the after-cart page to some degree, but nothing I’ve found so far lets me add products that aren’t physical or downloadable.