Use config to deploy web.config failed on access denied

Hi,

I try to use config into a compose file deployed with stack to deploy web.config.

version: '3.3'

services:
    myservice: 
        image: me/myimage:latest
        deploy:
            replicas: 1
            restart_policy:
                condition: on-failure
                delay: 10s
                max_attempts: 3
                window: 120s
        configs:
            - source: webconfig
              target: c:\App\Web.config
        volumes:
            - document:c:\App\Document
        ports:
            - "80:80"
        networks:
            - frontend
configs:
    webconfig:
        file: config/web.config
volumes:
    document:
networks:
    frontend:

My image is based on microsoft/windowsservercore:1709, install and configure IIS and launch a Powershell script as entrypoint that affect user rights to application pool user to app directory.
This command works

icacls C:\App /GRANT 'IIS AppPool\DefaultAppPool:F' /t /q /L;

but IIS throw a 500.19 error “cannot read configuration file due to insuffisient permissions”
If I try to apply directly to the config file

icacls C:\ProgramData\Docker\internal\configs /GRANT 'IIS AppPool\DefaultAppPool:F' /t /q;`

it returns “Access is denied”

I have no more idea on what I am doing wrong. Do you have a clue ?