In general, the subject matter described in this disclosure can be embodied in methods, systems, and program products. A server system receives a request for details regarding a product that a user of a remote computing device selected for purchase from a user interface provided by a third-party application program executable at the remote computing device. The received request specifies the product. The server system uses an indication of the product to identify details that are specific to the product. The server system sends, for receipt by the particular application program, the details. The server system receives, from the particular application program and after sending the details, confirmation to purchase the product, and, in response, sends a charge request to charge the user for the product to a transaction processing system.