Last modified: 2008-09-13 07:47:19 UTC
http://www.mediawiki.org/wiki/Manual:$wgProxyKey says "This feature has been deprecated and should not be used with current versions of MediaWiki. This feature was deprecated in version 1.4.0." However, go install fresh MediaWiki from scratch. There $wgProxyKey is. hardwired right in LocalSettings.php "sticking right in the users' face with no documentation".
This was fixed in r40355. LocalSettings no longer generates $wgProxyKey, it generates $wgSecretKey.
OK, but how are you going to get the message across to users during updates that they should change their LocalSettings.php to use the new variable? You could have update.php detect presence of the old variable and print a message surrounded by '***'s perhaps.
This was reverted anyway.