Hi @Steve Last ,
If you want to set app pool run as the user who's currently running the app, the only way is add user in windows user group. It cannot changed when application running, then user login. Even using impersonation.
What you can configure is the user who run the application. However, you don't want to use impersonation. So there's no useful methods to change user at IIS level. You need to set it in application by writing code.
So I recommend you to use authentication filter and authorization filter.
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Best regards,
Bruce Zhang