Add support for OpenBSD

[landryb]

OpenBSD has initial/wip wayland support, so add support for building/using swaylock on OpenBSD. It uses http://man.openbsd.org/auth_userokay for user authentication so integrates well with the various login methods.

There's no wordexp() on OpenBSD:

• it had security issues in the past (cf https://nvd.nist.gov/vuln/detail/CVE-2022-3008 &https://www.cvedetails.com/cve/CVE-2021-35942/)
• and it is generally considered a too dangerous/large hammer to solve small issues
  so i've written a small function to lookup for configuration files in the same paths, and i've tested that it was functionally equivalent.

been able to use swaylock with image=/usr/local/share/backgrounds/xfce/xfce-blue.jpg in ~/.config/swaylock/config swaylock and it does what's expected.

Feedback welcome !

[emersion]

Our wordexp usage is indeed an abuse I'd say. We've already removed it from Sway but the patches have not been backported to swaylock/swayidle: https://github.com/swaywm/sway/blob/020a572ed615b8fe272c7566a27ee0abe73a58d7/sway/config.c#L364

Can we just completely get rid of it?

[landryb]

Our wordexp usage is indeed an abuse I'd say. We've already removed it from Sway but the patches have not been backported to swaylock/swayidle: https://github.com/swaywm/sway/blob/020a572ed615b8fe272c7566a27ee0abe73a58d7/sway/config.c#L364

Can we just completely get rid of it?

oh definitely ! i see that wordexp() is still used in https://github.com/swaywm/sway/blob/020a572ed615b8fe272c7566a27ee0abe73a58d7/sway/config.c#L659 though, but i'll try to backport/reuse what was done in swaywm/sway@1d62d6bfa at least for the config path lookup, and i can also remove its use from the image path lookup if that's okay with you.

[emersion]

i see that wordexp() is still used

Yeah, that one is for include directives and is going to be much more tricky to drop because users do have env variable expansion and shell substitution in their config file (e.g. include $(uname -n)/*).

[landryb]

wordexp() usage dropped in 9c065d0 - i'll also backport the config bits to swaywm/swayidle#154, but i wouldnt know for the actual config lines parsing...