Hi Hao,
>> If I understand you correctly, I have to copy gluu configuration data to my existing openldap server?
Yes.
>> Is there any documentation for it?
Sorry, nothing public yet. We have customers who did that and there are internal documentations. May be we will publish one for public access soon.
>> Can we somehow achieve this without storing user & attributes in Gluu? Otherwise, how can 'enroll' keep an up-to-date attributes (for users who already exists in Gluu), whenever there is update in external IDP?
Yes, there is should some value like 'not_enrolled' or something like that which won't save data. We might need to tweak [script](https://github.com/GluuFederation/oxAuth/tree/master/Server/integrations/asimba) a bit for that.