Quick fix:
In file administrator/components/com_jaextmanager/lib/jaupdater/core/helper/NetworkHelper.php
In function "curl_getdata", add the following:
// Proxy configuration
$config = \JFactory::getConfig();
if ($config->get('proxy_enable')) {
curl_setopt($ch, CURLOPT_PROXY, $config->get('proxy_host') . ':' . $config->get('proxy_port') );
if ($user = $config->get('proxy_user')) {
curl_setopt($ch, CURLOPT_PROXYUSERPWD, $user . ':' . $config->get('proxy_pass') );
}
}
somewhere before the curl_exec.
Long-term fix would be to use the "system" functions instead of reinventing the wheel...
Greetings