How can I differ between local and remote login in WinForm App via VPN?

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remote

authentication

VPN

Hi,

I have a C# WinForm Database Application and I want to give my employees remote access from Home.
We have a V-DSL Internet connection by only with dynamic IP Address.
So I tried Team-Viewer a VPN-Remote Connection and it worked pretty well.

We also have a built-in user-management.
If the user logs-in from remote, than he shall only have restricted user right to our application.

Question:
How can the application get known if the user logs-in from a local Intranet PC or over VPN from an external PC?

Has anyone any idea how to solve that problem?
Is there a better way to connect to our local Intranet from outside without VPN, but with V-DSL with dynamic IP´s on both sides?

Best regards,

Rene