code: private static void copyDeprecatedConfigurationOptions(Configuration config) {
      copyIfNotPresent(
          config,
          GoogleHadoopFileSystemConfiguration.AUTH_SERVICE_ACCOUNT_ENABLE.getKey(),
          AUTHENTICATION_PREFIX + HadoopCredentialConfiguration.ENABLE_SERVICE_ACCOUNTS_SUFFIX);
      copyIfNotPresent(
          config,
          GoogleHadoopFileSystemConfiguration.AUTH_SERVICE_ACCOUNT_KEY_FILE.getKey(),
          AUTHENTICATION_PREFIX + HadoopCredentialConfiguration.SERVICE_ACCOUNT_KEYFILE_SUFFIX);
      copyIfNotPresent(
          config,
          GoogleHadoopFileSystemConfiguration.AUTH_SERVICE_ACCOUNT_EMAIL.getKey(),
          AUTHENTICATION_PREFIX + HadoopCredentialConfiguration.SERVICE_ACCOUNT_EMAIL_SUFFIX);
      copyIfNotPresent(
          config,
          GoogleHadoopFileSystemConfiguration.AUTH_CLIENT_ID.getKey(),
          AUTHENTICATION_PREFIX + HadoopCredentialConfiguration.CLIENT_ID_SUFFIX);
      copyIfNotPresent(
          config,
          GoogleHadoopFileSystemConfiguration.AUTH_CLIENT_SECRET.getKey(),
          AUTHENTICATION_PREFIX + HadoopCredentialConfiguration.CLIENT_SECRET_SUFFIX);
  
      String oauthClientFileKey =
          AUTHENTICATION_PREFIX + HadoopCredentialConfiguration.OAUTH_CLIENT_FILE_SUFFIX;
      if (config.get(oauthClientFileKey) == null) {
        // No property to copy, but we can set this fairly safely (it's only invoked if client ID,
        // client secret are set and we're not using service accounts).
        config.set(
            oauthClientFileKey, System.getProperty("user.home") + "/.credentials/storage.json");
      }
    }
docs: Copy deprecated configuration options to new keys, if present.