This plugin has been moved in to the core IdP distribution as of V2.3 and this documentation does NOT apply to the built-in version. ECP support is enabled by default in the configuration files that are shipped with V2.3 provided that container or web server authentication is enabled for the profile path of /idp/profile/SAML2/SOAP/ECP so that REMOTE_USER is set. More at IdPEnableECP.