Windows Authentication to AD group with Resources mapped from different server

Hi, This is my problem.

In my IIS 8.5 i have created a site(Just HTML files and Images) which is connected to a remote server. The connection is made using a specific service account. The application pool also runs with the same service account. Only this service account has access to te remote content.

Now i need to provide windows authentication to this  contents restricted to only a specific AD group. I tried enabling the windows authentication and authorization rules like below.

<security>

<authorization>

<add accessType="Allow" users="Domain\AD group />

</authorization>

<authentication>

<windowsAuthentication enabled="true" />

<anonymousAuthentication enabled="false" />

</authentication>

</security>

This is not working. I tried with specific users etc etc. Also i tried giving the app pool identity allow access to the Authorization rules. No Luck

Please help