bug#63198: cups-service-type uses PAM-enabled 'cups' by default which prevents authentication

[Maxim Cournoyer]

Hi,

Today I encountered an issue where after re-installing a Guix System, I
couldn't add a new printer anymore.  Any CUPS client (including the
trusty localhost:631 HTTP page) would loop on authenticating my user.

After consulting the logs and finding this kind of line:

--8<---------------cut here---------------start------------->8---
pam_authenticate() returned 7 (Authentication failure)
--8<---------------cut here---------------end--------------->8---

I started looking at our PAM configuration for CUPS, but we currently
have none, which is probably the issue.  Using 'cups-minimal' instead of
cups (which is built with linux-pam) solves the issue, as the 'cups'
value provided to the <cups-configuration> record.

We should probably make cups-minimal the default, or extend our
pam-service-type with the relevant PAM entries.

Thoughts/takers?

-- 
Thanks,
Maxim