code: public static UserGroupInformation readFrom(Configuration conf
        ) throws IOException {
      try {
        return UnixUserGroupInformation.readFromConf(conf,
          UnixUserGroupInformation.UGI_PROPERTY_NAME);
      } catch (LoginException e) {
        throw (IOException)new IOException().initCause(e);
      }
    }
docs: Read a {@link UserGroupInformation} from conf