In EAP 5 or Tomcat, sessionIdLength can be configured in <Manager> component of context.xml. In EAP 7 or Undertow, session-id-length can be configured in undertow subsystem. It is missed only in EAP 6 despite Manager MBean has setSessionIdLength() method. Easier way to configure it is expected just like "org.apache.catalina.session.StandardManager.MAX_ACTIVE_SESSIONS" system property for maxActiveSessions.
Created attachment 1136935 [details] patch 7.5.x property added to setup session-id-length. org.apache.catalina.session.ManagerBase.SESSION_ID_LENGTH no upstream required as this is supported through the jboss-web.xml configuration.
Verified with EAP 6.4.8.CP.CR2
Retroactively bulk-closing issues from released EAP 6.4 cumulative patches.