docs: public static void obtainTokenForJob(final RestClient client, User user, Job job) {
          Token<EsTokenIdentifier> token = obtainToken(client, user);
          if (token == null) {
              throw new EsHadoopException("No token returned for user " + user.getKerberosPrincipal().getName());
          }
          Text clusterName = token.getService();
          if (LOG.isDebugEnabled()) {
              LOG.debug("Obtained token " + EsTokenIdentifier.KIND_NAME.toString() + " for user " +
                      user.getKerberosPrincipal().getName() + " on cluster " + clusterName.toString());
          }
          job.getCredentials().addToken(clusterName, token);
      }