[keycloak-user] Using impersonation API to obtain token for public client

Hi! I have webapp1 which has to authenticate against a legacy backend,and won't be integrated with Keycloak for the foreseeable future. So, upon successful authentication, i use the impersonate API to get an access token for the current user. Later on, the user will open webapp2 from webapp1. The user should not have to perform a login in Webapp2. Webapp2 uses the Keycloak Javascript adapter. I use the access/refresh token i gained earlier to initialize the adapter. It sends the refresh token to the token endpoint, but gets a statuscode 400 error "Unmatching clients". Request: grant_type=refresh_token refresh_token=<encoded token> client_id=webapp2 These are the relevant fields from the token: aud: "webapp2" azp: "impersonator" So i guess the problem is, that azp does not match client_id. In order to get a token for the correct client, i use the token exchange endpoint and the access token i got via the impersonation API map.add("client_id", impersonator) map.add("client_secret", <impersonator_secret>) map.add("grant_type", "urn:ietf:params:oauth:grant-type:token-exchange") map.add("subject_token",<access token>) map.add("audience", "webapp2") That gives me a new token, but for the same client. At this point i'm stumped and pretty sure i misunderstood something basic. Can anybody give me a pointer in the right direction? Cheers, Till