Network configuration with automatic proxy configuration URL

??? My computer is behind a proxy server and the browser settings are configured by an automatic proxy configuration URL …/proxy.pac (I know the IP address of the “…” ) and username&password authorisation is required. Moreover, it’s connected using VPN. So how do I configure avast’s network settings? Upon installing it prevents VPN connection to occur. I tried even to stop Network shield and Web shield, leaving only Standard but it didn’t help.