debian/postrm: Remove /etc/pam.d/gdm-authd

[adombeck]

Having /etc/pam.d/gdm-authd around when authd was uninstalled breaks GDM.

Closes #1171
UDENG-8726

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.65%. Comparing base (6ff09d2) to head (8d76be8).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1172      +/-   ##
==========================================
+ Coverage   87.64%   87.65%   +0.01%     
==========================================
  Files          90       90              
  Lines        6222     6222              
  Branches      111      111              
==========================================
+ Hits         5453     5454       +1     
+ Misses        713      712       -1     
  Partials       56       56              

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[adombeck]

Tested by downloading the
authd_0.5.6+git251217+1410+3ba70e2b\~24.04.1_amd64.deb from the CI artifacts and installing and uninstalling it on Noble. Works as expected.

[3v1n0]

Well, technically apt remove should not remove config files as this one is (as someone may also have customized it), but we should rather just modify it so that we do not fail if the module is not there.

At the time I did not it on purposes since I wanted to be sure that we did not end up ignoring authd module, but this should still never happen.

So I'd just go with:

diff --git a/debian/authd.gdm-authd.pam b/debian/authd.gdm-authd.pam
index 32e8bb66a..2c6000f50 100644
--- a/debian/authd.gdm-authd.pam
+++ b/debian/authd.gdm-authd.pam
@@ -1,6 +1,6 @@
 #%PAM-1.0
 auth    [success=ok user_unknown=ignore default=bad] pam_succeed_if.so user != root quiet_success
-auth    [success=1 ignore=ignore default=die authinfo_unavail=ignore] pam_authd.so
+auth    [success=1 ignore=ignore default=die authinfo_unavail=ignore module_unknown=ignore] pam_authd.so
 # If authd ignored the request => local broker is selected,
 # then we continue with normal stack
 auth    substack        common-auth