param($url = "www.google.de",$key = "Vary",$desiredValue ="")
$Content = (Invoke-WebRequest -UseBasicParsing -Uri $url)

if($Content.Headers.$key -eq $desiredValue){
    Write-Host ("0:Key {0} holds the desired value {1}" -f $key,$desiredValue); exit 0;
}
else{
    Write-Host ("0:Key {0} doesn't hold the desired value! Current value: {1}" -f $key,$Content.Headers.$Key); exit 2;
}