Allow agnostic environment configuration in theme

Context :

In our themes customizations, we needs to add a standalone registration workflow thanks to a link in login page.

So, we need to manage an url (targeting frontend url) for our button in our custom theme.

Actually, the Keycloak beans presents in the freemarker context (https://github.com/keycloak/keycloak/tree/master/services/src/main/java/org/keycloak/forms/login/freemarker/model) doesn't contains a redirectUrl variable that we can handle (redirectUrl or whatever which would allow us to handle a frontend redirection)
Our workaround is to manage the redirection thanks to a reverse proxy (an /app
path is declared into properties files and handle by the reverse proxy) but it would be great that themes handle this usecase for a better maintenability by

• providing a way to use ENVIRONMENT VARIABLEs in freemarker Template thanks to ${env.VAR} for example ?
• providing full informations about the clients, including redirectUrl to easily redirect users ?
• providing a way to externalize configurations for a theme ?

Thanks