Hi,
I am not to sure, how you have to set up fireall rules in 1.2.3 because, like you mentioned, I am using 2.0 RC-1.
But in the rule you have to set:
protocol: tcp/udp
source port: any
source address: any (or LAN Subnet)
destination port: HTTPSall
destination address: any
GATEWAY: WAN1 Failover OR WAN2 Failover
But I would add the IPsec (500), ESP (4500), OpenVPN (1194) and PPTP (1723) ports to your Alias httpsall, too. You could have a look at wikipedia and VPN and find out, which method is using which port and then add it to https.
Like your alias is looking at the moment, ther will be no difference for VPN connections than without an Alias.