XEP-0257 (Client Certificate Management for SASL EXTERNAL) has been Deferred because of inactivity.
Abstract: This specification defines a method to manage client certificates that can be used with SASL External to allow clients to log in without a password. URL: http://www.xmpp.org/extensions/xep-0257.html If and when a new revision of this XEP is published, its status will be changed back to Experimental.
