Methods and systems provide for sharing information between computer networks in which the information to be shared is required at one location (e.g. for the provision of a data-processing service) but is only available at a separate location. The information may be deliberately absent (e.g. for privacy reasons) or may be unavailable as an artifact of the computer network(s) involved. For the provision of a data-processing service, where several different devices on one network may service contiguous requests from a client device on another network according to a load-balancing strategy, data is propagated once only through the service network. Network communication software is subsequently amended to provide the minimal information necessary for a device on the service network to retrieve the information pertinent to the client device and necessary for its service. Therefore, a web-based single sign-on scheme can operate over HTTP to authorize data-processing services, such as web-filtering services.