[keycloak-user] Authentication (Node.JS) Microservice to pass User x.509 certificate to Keycloak

Hi! I am currently trying to have a Node.JS application between the User and Keycloak. Keycloak is running in a Docker container (with the option "-e PROXY_ADDRESS_FORWARDING=true"). The Node.JS microservice connects to Keycloak via HTTPS and wants to offer the User x.509 certificate. How do I have to configure Keycloak (Docker image) to accept the user cert? - certificate is PEM - we have a CA set up and can provide the ca-chain - Node.JS currently tries connecting via 'isomorphic-fetch' and passing cert in headers... All I get so far with headers: - SSL_CLIENT_CERT - X-Client-Certificate - USER_CERT - javax.servlet.request.X509Certificate --> { error_description: 'X509 client certificate is missing.', error: 'invalid_request' } Thank you sincerely! Daniel