Authentication and Authorization for services is quite huge topic and there are many subtle details that should be taken in account in order to implement the right solution.
Data Services generated by Add OpenAccess Service
wizard are not different than the ones that you can generate following the guidance from Microsoft so I suggest that you check these sets of articles to see which scenario described there matches your specific needs:
I hope that these resource will help you achieve the results you wanted. If you need any further assistance you can write back to us your questions.
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