@hmkwon@lgcns.com Apologies for the delay in response and all the inconvenience caused because of the issue.
You can refer to below issue with the same exception on different Azure issue which might be helpful in your use case:
https://github.com/Azure/azure-sqldb-spark/issues/28
The above discussion might be helpful for you to give your pointers to resolve the issue.
Also I would encourage you to open SDK related issue on GitHub here.We do have our Product Group Team working on issues on SDK and can help you out better with your issues.
Hope it helps!!!
Please "Accept as Answer" if it helped so it can help others in community looking for help on similar topics.