public SecurityManager getSecurityManager() {
        return securityManager;
    }
Gets the application {@code SecurityManager} instance to be used by the constructed Shiro Filter.  This is a
required property - failure to set it will throw an initialization exception.

@return the application {@code SecurityManager} instance to be used by the constructed Shiro Filter.
support/spring/src/main/java/org/apache/shiro/spring/web/ShiroFilterFactoryBean.java