Methods and systems are provided for making secure financial transactions, such as purchase payments, using rich Internet applications (RIA) running an RIA runtime (also referred to as a platform or framework) on the user's smart phone or other mobile device. Embodiments differ from the usual way of re-directing a user from a third-party application and authenticating the user by providing secure in-line payments from a rich Internet application running on an RIA runtime. A system includes: a mobile device executing a rich Internet application running on an RIA runtime; a payment library communicating with the RIA runtime and a service provider, for which the payment library communicates with the service provider to authenticate the rich Internet application; and in response to authentication by the service provider, facilitates secure financial transactions via the rich Internet application.