[keycloak-user] Token exchange: on-behalf-of + downgrade

Hello guys. I would like to ask you help with the following. I’m currently looking at on-behalf-of scenario with Keycloak. In this case we have ‘web app’ calling ’svc-1’, which in turn calls another service ‘svc-2’. That is, we have: web —> svc-1 —> svc-2. The idea is to let svc-2 know who is actual initiator of the call chain (end-to-end identity propagation). The question is about how to do that with Keycloak. First, in order to propagate caller identity we could exchange tokens in ‘svc-1’. In this case we can have correct audience and, thus, control token usage. Second, we need is to remove any excessive permissions (client roles) that are not related to ‘svc-2’ call in order to reduce potential harm in case this token is intercepted by someone. And if I know how to exchange tokens, I cannot find how to downgrade the token during the exchange. As I see in documentation, ‘scope’ parameter is not supported for token exchange. So, my questions are: Is token exchange a right tool for this task? Is it possible to downgrade exchanged token? And how, if so? Thank you, Alexey