So Trust is configured and FAS was activated on the Storefront with the Powershell Command:
Get-Module "Citrix.StoreFront.*" -ListAvailable | Import-Module
$StoreVirtualPath = "/Citrix/XXX"
$store = Get-STFStoreService -VirtualPath $StoreVirtualPath
$auth = Get-STFAuthenticationService -StoreService $store
Set-STFClaimsFactoryNames -AuthenticationService $auth -ClaimsFactoryName "FASClaimsFactory"
Set-STFStoreLaunchOptions -StoreService $store -VdaLogonDataProvider "FASLogonDataProvider"
Storefront alone looks good