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Based on my understanding of your question above you want to obtain the log or registry of the users that use the VPN service.
I think you would be able to get this data via P2SDiagnosticLog where whenever a client will connect via IKEv2 or OpenVPN Point to Site, the table will log packet activity, EAP/RADIUS conversations and successful/failure results by user. Connection source info is provided for IKEv2 and OpenVPN connections only. To see these logs, you will have to enable diagnostic logging for your VPN Gateway.
If you wish to see the current active P2S sessions for you VPN Gateway, you can refer to this documentation.
https://learn.microsoft.com/en-us/azure/vpn-gateway/p2s-session-management
Hope this helps! Please let me know if you have any additional questions. Thank you!
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