I recently did an `aptitude upgrade` and Apache 2.0.something got upgraded to 2.2.something. This broke one of my sites which requires SSL and a username and password. The error was something to the tune of “Invalid command ‘AuthDigestFile’, perhaps misspelled or defined by a module not included in the server configuration.”
Well, apparently the name of this directive has changed to AuthUserFile. At least, changing it allowed the server to start and the expected functionality returned. Hopefully it has not opened up a big gaping security vulnerability.
The Apache Wiki also has something to say about it.