docs: private void putCred(String key, EsToken token, Map<String, String> credentials) {
          FastByteArrayOutputStream stream = new FastByteArrayOutputStream();
          DataOutput output = new DataOutputStream(stream);
          try {
              token.writeOut(output);
          } catch (IOException e) {
              throw new EsHadoopException("Could not serialize EsToken", e);
          }
          String credential = new String(Base64.encodeBase64(stream.bytes().bytes()), StringUtils.UTF_8);
          credentials.put(key, credential);
      }