Description

Add customizable "header" (or disclaimer) to keycloak.v2 login theme (similar to footer that was added for 26.0.0).

Discussion

No response

Motivation

Many sites require the user to be aware of certain facts via a disclaimer (data export, privacy, intellectual property, etc.). Currently we have to override the entire login.ftl in the keycloak.v2 login theme to add a disclaimer that is shown to all users before login. This create maintenance issues on Keycloak version upgrades. However, if we could just override a header.ftl (like the just-added footer.ftl), this would make version upgrades seamless in the future when it comes to themes (usually our biggest headache).

Details

I'll be happy to create a PR for this.