Altere o arquivo deploy/jmx-console.war/WEB-INF/web.xml, removendo as tags abaixo da sessão security-constraint:
<http-method>GET</http-method>
<http-method>POST</http-method>
Deve ficar parecido com isso:
<security-constraint>
<web-resource-collection>
<web-resource-name>HtmlAdaptor</web-resource-name>
<description>
An example security config that only allows users with the role
JBossAdmin to access the HTML JMX console web application
</description>
<url-pattern>/*</url-pattern>
</web-resource-collection>
<auth-constraint>
<role-name>JBossAdmin</role-name>
</auth-constraint>
</security-constraint>
Agora reinicie sua instância.
Mais detalhes/Referências: