WildFly Security Domains
Internal
Overview
A security domain is a set of Java Authentication and Authorization Service (JAAS) declarative security configurations used by one or more applications to control authentication, authorization and security auditing. An application specifies a security domain to manage its security information. Security domains are declared as part of the security subsystem. A security domain is a JBoss concept that predates the security realm, which was introduced in JBoss 7 and then WildFly.
Security domains are declared in the JBoss configuration files (domain.xml or standalone.xml) as part of the security subsystem. Since the security domains are part of the security subsystem, they are loaded after core services.
Users can create custom security domains, as shown here Adding a New Security Domain