add AUTH_STATUS_CHANGED event

JitsiConference.js

     conference.room.addListener(AuthenticationEvents.IDENTITY_UPDATED, function (authEnabled, authIdentity) {
         conference.authEnabled = authEnabled;
         conference.authIdentity = authIdentity;
+        conference.eventEmitter.emit(JitsiConferenceEvents.AUTH_STATUS_CHANGED, authEnabled, authIdentity);
     });
 
     conference.room.addListener(XMPPEvents.MESSAGE_RECEIVED, function (jid, displayName, txt, myJid, ts) {

JitsiConferenceEvents.js

     /**
      * Indicates that available devices changed.
      */
-    AVAILABLE_DEVICES_CHANGED: "conference.availableDevicesChanged"
+    AVAILABLE_DEVICES_CHANGED: "conference.availableDevicesChanged",
+    /**
+     * Indicates that authentication status changed.
+     */
+    AUTH_STATUS_CHANGED: "conference.auth_status_changed"
 };
 
 module.exports = JitsiConferenceEvents;

doc/API.md

         - STARTED_MUTED - notifies that the local user has started muted
         - AVAILABLE_DEVICES_CHANGED - notifies that available participant devices changed (camera or microphone was added or removed) (parameters - id(string), devices(JS object with 2 properties - audio(boolean), video(boolean)))
         - CONNECTION_STATS - New local connection statistics are received. (parameters - stats(object))
+        - AUTH_STATUS_CHANGED - notifies that authentication is enabled or disabled, or local user authenticated (logged in). (parameters - isAuthEnabled(boolean), authIdentity(string))
 
     2. connection
         - CONNECTION_FAILED - indicates that the server connection failed.