Connecting Through a Firewall or Proxy
To connect through the Windows system proxy, set only the connection properties needed to authenticate and connect. To connect to other proxies, set ProxyAutoDetect to false and in addition set the following.
To authenticate to an HTTP proxy, set ProxyAuthScheme, ProxyUser, and ProxyPassword, in addition to ProxyServer and ProxyPort.
To connect to other proxies, set FirewallType, FirewallServer, and FirewallPort. To tunnel the connection, set FirewallType to TUNNEL. To authenticate to a SOCKS proxy, set FirewallType to SOCKS5. Additionally, specify FirewallUser and FirewallPassword.