IIS 7 Grant user permissions

In IIS6 and IIS7, the equivalent for ASP.NET to the ASPNET user is the application pool identity user. By default that's NETWORK SERVICE in IIS7, and the App Pool identity in IIS 7.5+. You can grant that user permissions to disk and it will work.

The 'better' way is to create custom users per app pool and assigning them permission to disk so that the sites are isolated from each other, and so that other applications on the server that use Network Service can't access the content of your sites. However that's a judgment call that you need to make in your situation.

The other user that comes into play is the anonymous or authenticated user of your site. That's defined in the authentication -> anonymous section of your site. In IIS7 I recommend setting that to use the app pool identity, as long as you only have 1 site per pool, or as long as each site in the app pool highly trust each other. Then you only need to maintain 1 user on disk.

Please refer to the article Building Secure ASP.NET Applications: Authentication, Authorization, and Secure Communication.

This will give you a better understanding on the identity used by your ASP.NET application when impersonating. Give the necessary permission and you are good.

HTH