@Override
  public int addMasterKey(String s) {
    int keySeq = masterKeySeq.getAndIncrement();
    LOG.trace("addMasterKey: s = {}, keySeq = {}", s, keySeq);
    masterKeys.put(keySeq, s);
    return keySeq;
  }
Default in-memory token store implementation.
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/security/MemoryTokenStore.java