[keycloak-user] Custom error message in "Authenticator Execution" Script

Hi I'm trying to create a Browser Authentication flow in Keycloak which rejects the user if it does not have the required role, however I am unable to show the user a customized message on a rendered error page. How does one show a custom error message defined in the script? I've been able to show custom error in JSON using the code below, however I would like it to be rendered using for example the error.ftl template i.e keycloak/themes/src/main/resources/theme/base/login/error.ftl AuthenticationFlowError = Java.type("org.keycloak.authentication.AuthenticationFlowError"); ErrorRepresentation = Java.type("org.keycloak.representations.idm.ErrorRepresentation"); Response = Java.type("javax.ws.rs.core.Response"); MediaType = Java.type("javax.ws.rs.core.MediaType"); function authenticate(context) {     /* CODE FOR AUTH CHECK */     if (authShouldFail) {         var errorRep = new ErrorRepresentation();         errorRep.setErrorMessage("You are not authorized to use this application");         var response = Response.status(401).entity(errorRep).type(MediaType.APPLICATION_JSON_TYPE ).build();         LOG.info(script.name + " failed auth for: " + username);         context.failure(AuthenticationFlowError.INVALID_USER, response);         return;     }     context.success(); }