Mechanisms for securely allowing a participant computing entity to engage in a transaction initiated by an initiator computing entity and managed by a coordinator computing entity. The initiator provides a transaction initiation request to the coordinator. Upon receipt, the coordinator accessing a transaction coordination context that includes information such as a secure key that may be used by a participant to register in the transaction. The coordinator then provides the coordination context to the initiator, which provides the coordination context to the participant(s) that are also to engage in the transaction. Each participant then generates a registration request that is based on the coordination context, and that is secured using the secure key provided in the coordination context.