Is it possible to provide logins based on purchases?
YOu don't need a real login, just an access to a certain node. For this, you can use the Node autorize link module:


  Generates link for view, edit, or delete content without login


So, when someone pruchases something you must create a node tieh the data tue user can view. Add the view authorize link to the purchase email notification and the customer will have access to the node with data just following the emailed link.