A method is presented for transferring data objects between federated entities within a federated computational environment using artifacts. A first federated entity receives artifacts from a second federated entity that generates data objects, such as assertions, for use at or by the first federated entity. An artifact references a data object that is locally stored by the second federated entity, which is implemented as a distributed system having multiple data processing systems, each of which can generate artifacts and associated data objects and can proxy retrieval requests to systems within the second federated entity. Each artifact includes a tag that indicates the data processing system within the second federated entity that generated the artifact. When the second federated entity receives a retrieval request with an artifact from the first federated entity, the appropriate data object is retrieved from within the distributed data processing system using the artifact and the tag.