Newbie help wanted : WAN behind proxy with authentication

[phs_opnsense]

I am giving OPNsense a tryout . I installed it in a VMware ESXi VM.

To access internet, my WAN needs to use a proxy (with basic Authentication) ... can someone help me, don't think there is something in the GUI (but I am ready to "mess" with cmdline as well).

I would like for a start to be able to check for updates and install the vmware plugin.