Allow separate URLs for authentication and admin pages

[br4n82]

While migrating my web-services to Pangolin, I had the thought it may help security to separate the authentication and admin pages into different URLs. This would enable users to restrict the admin dashboard to a private subdomain (like dash.domain.tld), with its DNS pointed to an internal Tailscale or Wireguard address that only they can access. Meanwhile, the authentication page could point to a public-facing subdomain (like proxy.domain.tld) accessible to external connections.