Verification e-mail URL configuration

[Jurjan-Paul Medema]

Hello!

I’m struggling to understand the documentation on this point: how do I configure the URL to be used in verification e-mails (now that we want to be able to trigger a password reset from another process from within the same private network in which Keycloak runs, so no longer invoking the API through the public URL, through nginx, etc.)?

Context: Keycloak 18.0.0, WildFly distribution.

I have tried to configure the `hostname` as a CLI parameter and as an environment variable (neither makes any difference: the verification e-mails contain a link to `localhost`, because that’s the host used in the request on the API) and also configured a `frontendUrl`. The latter broke login completely, possibly because I haven’t properly understood what is meant exactly by ‘base URL’ in
https://www.keycloak.org/docs/18.0/server_installation/index.html#_hostname 
and
https://github.com/keycloak/keycloak-containers/blob/18.0.2/server/README.md#specify-frontend-base-url.

So, given that the URL in the verification e-mail used to have (and should keep) the form
`https://subdomain.domain.ttl/auth/realms/our-realm-name/login-actions/action-token?key=lots-of-characters`,
can somebody please tell me what exactly should be configured (and where) to keep the verification e-mails working? Or point me to the specific documentation that addresses this question?

Thanks!
Jurjan-Paul Medema