<configuration>
    <authentication-client xmlns="urn:elytron:1.0">
        <authentication-rules>
            <rule use-configuration="auth-config"/>
        </authentication-rules>
        <authentication-configurations>
            <configuration name="auth-config">
                <sasl-mechanism-selector selector="DIGEST-MD5"/>
                <set-user-name name="user"/>
                <credentials>
                    <hashed-password algorithm="simple-digest-md5" hash="cGFzc3dvcmQ="/>
                </credentials>
            </configuration>
        </authentication-configurations>
    </authentication-client>
</configuration>

org.wildfly.client.config.ConfigXMLParseException: CONF0005: Unexpected element "authentication-client" in namespace "urn:elytron:1.0" encountered
	at vfs:/content/wildfly-config-xml.war/META-INF/wildfly-config.xml:15:5
	at org.wildfly.client.config.ConfigurationXMLStreamReader.unexpectedElement(ConfigurationXMLStreamReader.java:245)
	at org.wildfly.security.auth.client.ElytronXmlParser.parseAuthenticationClientConfiguration(ElytronXmlParser.java:197)
	at org.wildfly.security.auth.client.ElytronXmlParser.parseAuthenticationClientConfiguration(ElytronXmlParser.java:146)
	at com.redhat.eap.qe.elytron.authnctx.WildflyConfigXmlServlet.parseAndCreateAuthenticationClientConfiguration(WildflyConfigXmlServlet.java:120)
	... 41 more

<clear-password password="password"/>