Recreating issue as described at:
gradle clean build
java -jar build/libs/boot-autoconfig-issue.jar
Failure during startup:
java.lang.NoClassDefFoundError: org/springframework/security/web/authentication/switchuser/AuthenticationSwitchUserEvent
SecurityAutoConfiguration is disabled in app.groovy so I would expect that even though Spring Security is transitively included in runtime classpath due to dependency on Spring-WS-Sec that Spring Boot would not attempt to initialize Security.