it seems docs in http://docs.jboss.org/keycloak/docs/1.2.0.CR1/userguide/html/server-installation.html#d4e115 should note about adding 4th element:

<subsystem xmlns="urn:jboss:domain:keycloak:1.0">
<auth-server name="main-auth-server">
<enabled>true</enabled>

<web-context>auth</web-context>
</auth-server>
</subsystem>