standalone.xsl

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:xalan="http://xml.apache.org/xalan"
                xmlns:j="urn:jboss:domain:1.3"
                version="2.0"
                exclude-result-prefixes="xalan j">

    <xsl:param name="config"/>

    <xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes" xalan:indent-amount="4" standalone="no"/>
    <xsl:strip-space elements="*"/>

    <xsl:template match="node()[name(.)='datasources']">
        <xsl:copy>
            <xsl:apply-templates select="node()|@*"/>
            <datasource jndi-name="java:jboss/datasources/KeycloakDS" pool-name="KeycloakDS" enabled="true" use-java-context="true">
                <connection-url>jdbc:h2:${jboss.server.data.dir}/keycloak;AUTO_SERVER=TRUE</connection-url>
                <driver>h2</driver>
                <security>
                    <user-name>sa</user-name>
                    <password>sa</password>
                </security>
            </datasource>
        </xsl:copy>
    </xsl:template>

    <xsl:template match="@*|node()">
        <xsl:copy>
            <xsl:apply-templates select="@*|node()" />
        </xsl:copy>
    </xsl:template>

</xsl:stylesheet>