A processing error will show the error page ./keycloak/themes/base/login/error.ftl
But in case of a possible internal error, the client data are not available
and the <a href> section is not shown, because of check <#if client?? && client.baseUrl?has_content>
To point the user to any action, an <#else> branch is requiert.
I added as PoC such message part in case client data are not available:
The message bundles will conatin the new backGeneral message:
How to produce an internal error, where client data are empty? take a look at KEYCLOAK-13305 where Keycloak runs with MySQL and utf-8 characterset, but user enters character included in utf8mb4 characterset