As a requirement for accessing Service B, Service A needs to encrypt its request message. Service B decrypts the message, makes some changes, encrypts the message, and then forwards it to Service C. However, the message does not make it to Service C. Instead, a runtime error is raised by a service agent that does not support encryption. This service agent only requires access to the message header in order to route the message to the appropriate instance of Service C. It is therefore decided that the header part of the message will not be encrypted. Which of the following can be used to address this requirement?