@depth9mcd This is typically accomplished using a proxy (Apache, NGINX, etc) in front of FusionAuth.
https://fusionauth.io/docs/v1/tech/admin-guide/proxy-setup#proxies-and-tenants has more details.
However, please feel free to file a feature request with your suggestion for a lambda to run before the authorize page is rendered: https://github.com/fusionauth/fusionauth-issues/issues