Kerberos server guide: Do not use kerberos_example in documentation

[Claudio Kuenzler]

On the official and up to date Kerberos server guide page (https://help.ubuntu.com/lts/serverguide/kerberos.html), the last section uses the following command snippet:

sudo auth-client-config -a -p kerberos_example

Using this kerberos_example is a very bad idea as it will allow any local user to become root without additional authentication!

This should definitely be changed to something secure, as a lot of people (unfortunately) follow such guides in a blind manner.

For more information, see
- https://www.claudiokuenzler.com/blog/874/local-users-becoming-root-using-su-without-password-authentication-wrong-config
- https://bugs.launchpad.net/ubuntu/+source/auth-client-config/+bug/526999.

[Andreas Hasenack (ahasenack)]

Thanks for filing this bug. I'm in the process of rewriting/checking the guides, and kerberos is in the list. I added this bug to my list of things to check.

[Andreas Hasenack (ahasenack)]

This doesn't affect focal, since auth-client-config isn't in the archive anymore. But the docs should be clarified for bionic.

[Andreas Hasenack (ahasenack)]

I updated the guide at https://discourse.ubuntu.com/t/service-kerberos/11331

That chapter has a section on client authentication which I also updated.

[Doug Smythies (dsmythies)]

Why did you set this to "fix released" for bionic? It hasn't been fixed.