+* Massive overhaul to session handling:
+** $wgSessionsInObjectCache is no longer supported and must be true, due to
+ MediaWiki\Session\SessionManager. $wgSessionHandler is similarly no longer
+ used.
+** ObjectCacheSessionHandler is removed, replaced with
+ MediaWiki\Session\PhpSessionHandler.
+** PHP session handling in general ($_SESSION, session_id(), and so on) is
+ deprecated. Use MediaWiki\Session\SessionManager instead. A new config
+ variable, $wgPHPSessionHandling, is available to cause use of $_SESSION to
+ issue a deprecation warning or to cause most PHP session handling to throw
+ exceptions.
+** Deprecated UserSetCookies hook. Session-handling extensions should generally
+ be creating a custom subclass of CookieSessionProvider. Other extensions
+ messing with cookies can no longer count on user data being saved in cookies
+ versus other methods.
+** Deprecated UserLoadFromSession hook, extensions should create a
+ MediaWiki\Session\SessionProvider.
+** The User cannot be loaded from session until after Setup.php completes.
+ Attempts to do so will be ignored and the User will remain unloaded.
+** CSRF tokens may be fetched from the MediaWiki\Session\Session, which uses
+ the MediaWiki\Session\Token class.
+* MediaWiki will now auto-create users as necessary, removing the need for
+ extensions to do so. An 'autocreateaccount' right is added to allow
+ auto-creation when 'createaccount' is not granted to all users.
+* Deprecated AuthPluginAutoCreate hook in favor of LocalUserCreated.
+* Most cookie-handling methods in User are deprecated.
+* $wgAllowAsyncCopyUploads and $CopyUploadAsyncTimeout were removed. This was an
+ experimental feature that has never worked.
+* Login and createaccount tokens now vary by timestamp.
+* LoginForm::getLoginToken() and LoginForm::getCreateaccountToken()
+ return a MediaWiki\Session\Token, and tokens must be checked using that
+ class's methods.