[keycloak-user] Mapping identity provider ID (sub) to user attribute

Hi. I have setup a realm using another keycloak as OIDC identity provider. So we have a setup:  client —> keycloak A <—> keycloak B Where we control A but not B. Since we have a custom integration with this provider from before, I need to get the id of the provided identity (B.sub) into the access token produced by A to remain backward compatible with our data. To accomplish this, I followed the outline from: https://lists.jboss.org/pipermail/keycloak-user/2017-October/012132.html where a mapper (“Attribute importer”) is added to the identity provider, which should import claim ‘sub’ as a user attribute. We would then import claim ‘sub' into user attribute ‘sub', then for the client, map user attribute ’sub' to claim ‘provider_id' in access token. However, no value is imported from the identity no matter which claims or attribute I map to/from. Only the hardcoded values seem to show up when I list the attributes of the user in the admin console. Can anyone confirm if this should work, and what I should try next? I have tried importing claim sub from provided identity into many different custom user attributes to no avail.