Hi Qin,
>> When register client into Gluu, it will return "oxd_id", but the "oxd_id" can become invalid as time passed
There is a default timestamp of client secret value for all clients which are registered dynamically in Gluu Server.
After registering your app in Gluu Server ( after completion of oxD registration ); try to change the 'Client Secret Expires' in associated client in Gluu Server.
Let's see if that can resolve your issue.