btw: if anyone wants to take the time and write a standalone.xml->keycloak.conf parser, that would be more than nice. I will most likely not have the time to do it in the foreseeable future, but can surely help / provide guidance. So when somebody searches a valuable pet project in the keycloak ecosystem, feel free to reach out.😇

What exactly should this tool do?
I assume that you want to extract non-default keycloak-server config and transform the config to the new format.

Should this be a separate shell tool?
Perhaps a simple jbang script will do the job here.
(It's probably just for wildfly or also jboss eap)?

Right. Would be nice if you could just do kc.sh tools migrate-config --file=<your-legacy-standalone.xml> and you get a valid keycloak.conf file containing all your customizations out of it, wouldn't it? Best would be wildfly and eap, for sure.

I'd love to be proven wrong here, but I have my doubts that it is realistic to build a tool that can migrate standalone.xml in a meaningful way.

@thomasdarimont @dasniko Could you please check if this new guide helps you? See #10401.

I'd assume from the docs (#10401) it will be
spi-custom-username-password-form-self-registration-url=http://example.com/register
and
KC_SPI_CUSTOM_USERNAME_PASSWORD_FORM_SELF_REGISTRATION_URL=http://example.com/register

selfRegistrationURL is camel-case and thus would change to - as separator and lower case, for envvars all is uppercase and - turns into _.
But I'm not sure about the URL part, will it stay url or will it become u-r-l? 🤔

Thanks Niko, but that didn't work.
I also tried with property renamed to "self-registration-url" and "selfregistrationurl".
No success.
I wonder how Keycloak recognizes where the provider name ends and the property name starts if everything is filled with dashes.

What eventually was successful:
KC_SPI_AUTHENTICATOR_CUSTOM_USERNAME_PASSWORD_FORM_SELFREGISTRATIONURL=http://example.com/register
for property name "selfregistrationurl" used inside the factory init method.
And also
KC_SPI_AUTHENTICATOR_CUSTOM_USERNAME_PASSWORD_FORM_SELF_REGISTRATION_URL=http://example.com/register
for property name "self-registration-url".

Ok, from your example it wasn't obvious that it's an authenticator SPI and I completely missed the part of the SPI-ID.

Because it wasn't obvious from the original example that the spi was "authenticator", here's the summary how it works:
Old Wildfly style configuration in standalone.xml:

<spi name="authenticator">
    <provider name="custom-username-password-form" enabled="true">
        <properties>
            <property name="selfRegistrationURL" value="http://example.com/register"/>
        </properties>
    </provider>
</spi>

New style configuration:
KC_SPI_AUTHENTICATOR_CUSTOM_USERNAME_PASSWORD_FORM_SELF_REGISTRATION_URL=http://example.com/register

This even works with camel-case property name "selfRegistrationURL"!