@Nonaxium,
It might help to actually say what NAC solution you are using. There's some rather large differences between quarantine configuration between NAC solutions, so knowing how your NAC solution is actually attempting to route to the authentication page would be good to know. Some solutions have you use the NAC appliance as the DNS server for the quarantine VLAN, and others are expecting you to forward all traffic to the NAC authentication page through a proxy.
When it comes to routing on the PAN side, that's going to depend on the rest of your network configuration and how you have things setup. In some situations you could just use a simple static route because the quarantine VLAN is terminating on a dedicated PAN interface, and in others you'll have to use a PBF so that you can capture just the addresses that you are looking for. The firewall isn't going to proxy and redirect the URL to your NAC auth page if that's a requirement however.
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