code: private static Optional<Token<?>> getTokenFromSeqFile(String authPath, String proxyUserName) throws IOException {
      try (Closer closer = Closer.create()) {
        FileSystem localFs = FileSystem.getLocal(new Configuration());
        SequenceFile.Reader tokenReader =
            closer.register(new SequenceFile.Reader(localFs, new Path(authPath), localFs.getConf()));
        Text key = new Text();
        Token<?> value = new Token<>();
        while (tokenReader.next(key, value)) {
          LOG.info("Found token for " + key);
          if (key.toString().equals(proxyUserName)) {
            return Optional.<Token<?>> of(value);
          }
        }
      }
      return Optional.absent();
    }
docs: Get token from the token sequence file.
  @param authPath
  @param proxyUserName
  @return Token for proxyUserName if it exists.
  @throws IOException