class AuthorisationDirective implements SchemaDirectiveWiring {

        @Override
        public GraphQLFieldDefinition onField(SchemaDirectiveWiringEnvironment<GraphQLFieldDefinition> environment) {
            String targetAuthRole = (String) environment.getDirective().getArgument("role").getArgumentValue().getValue();

            //
            // build a data fetcher that first checks authorisation roles before then calling the original data fetcher
            //
            DataFetcher originalDataFetcher = environment.getFieldDataFetcher();
            DataFetcher authDataFetcher = new DataFetcher() {
                @Override
                public Object get(DataFetchingEnvironment dataFetchingEnvironment) throws Exception {
                    Map<String, Object> contextMap = dataFetchingEnvironment.getContext();
                    AuthorisationCtx authContext = (AuthorisationCtx) contextMap.get("authContext");

                    if (authContext.hasRole(targetAuthRole)) {
                        return originalDataFetcher.get(dataFetchingEnvironment);
                    } else {
                        return null;
                    }
                }
            };
            //
            // now change the field definition to have the new authorising data fetcher
            return environment.setFieldDataFetcher(authDataFetcher);
        }