AuthDigestFile not working is not a bug. That directive was removed in Apache 2.2, as it was no longer necessary.
The directive isn't necessary, by the way. We've already got a bit in our web server configuration that blocks access to all files with names beginning with ".ht" (.htaccess, .htpasswd, .htdigest…).
What's probably really getting in the way here, though, is that the domain you're entering to htdigest ("guests") is incorrect. It needs to match the whole string in AuthName, which is a reason why I'd recommend against using that field for a notice if you're using digest authentication.
Here's a minimal two-step process to get digest authentication working for a folder called "/secure".
- Put this in .htaccess:
AuthName "Secure Files"
- Create the .htdigest file:
htdigest -c /home/username/example.com/secure/.htdigest "Secure Files" username
That's it! (You should, of course, replace "username", "example.com", "/secure", and "Secure Files" with appropriate values for your user and domain.)