code: public static UserGroupInformation getCurrentUGI() {
      try {
        // Check original caller's UGI in case call went through proxy
        UserGroupInformation origUGI = OrigUGI.get();
        if (origUGI != null) {
          return origUGI;
        }
        // If original caller's UGI is not set then we get the UGI of connecting client
        Call call = CurCall.get();
        if (call != null) {
          return call.connection.header.getUgi();
        }
      } catch (Exception e) { }
      return null;
    }
docs: Gives access to the subject of the current call.