A method and system for securely propagating client identities in a service call from a first system to a target service system are provided. The system includes a memory device for storing data and a service provider (SP) computer system. The SP computer system is programmed to determine identities to transmit to the target system in association with a request, construct a data structure to represent each identity and additional information related to the identity, digitally sign the identity information, pair the identity information and the corresponding digital signature in a header of a request message from the first system to the target service system, receive the request message and extract the identity information and corresponding digital signatures from the header, validate the corresponding digital signatures, and construct using the corresponding identity information a data structure that represents each of the original identities established in the first system.