A secure data broker has been developed, which provides a restricted message based data exchange between a client application and a secured information resource by allowing registered or verified messages to be brokered across a security barrier. In some configurations, both requests and responses are validated and brokered across the security barrier. In other configuration, either requests or responses are validated. To support validation, messages are formatted in accordance with a predefined message specification for at least part of a transaction path between a client application and an information resource accessed by the client application.