feat(system/yubikey): implement PAM auth for Yubikey OTP

Signed-off-by: Matej Focko <me@mfocko.xyz>

roles/system/yubikey/defaults/main.yml

@@ -0,0 +1,9 @@
+---
+# Pair of ID and token that are used for verifying the Yubikey OTP against the
+# Yubico servers
+
+# Yubikey App ID for the PAM module
+system_yubikey_id: None
+
+# Yubikey App Token for the PAM module
+system_yubikey_key: None

roles/system/yubikey/tasks/install.yml

@@ -0,0 +1,18 @@
+---
+- name: Install ‹pam_yubico› on Fedora/EPEL
+  ansible.builtin.package:
+    name: pam_yubico
+    state: present
+  when: ansible_distribution in [ "AlmaLinux", "CentOS", "Fedora" ]
+
+- name: Enable PPA on Ubuntu
+  ansible.builtin.apt_repository:
+    repo: ppa:yubico/stable
+    state: present
+  when: ansible_distribution == "Ubuntu"
+
+- name: Install ‹libpam-yubico› on Ubuntu
+  ansible.builtin.package:
+    name: libpam-yubico
+    state: present
+  when: ansible_distribution == "Ubuntu"

roles/system/yubikey/tasks/main.yml

@@ -0,0 +1,12 @@
+---
+- name: Install packages
+  ansible.builtin.include_tasks: install.yml
+  tags: install
+
+- name: Set up PAM
+  ansible.builtin.template:
+    src: templates/yubikey-sufficient
+    dest: /etc/pam.d/yubikey-sufficient
+    mode: 0644
+    owner: root
+    group: root

roles/system/yubikey/templates/yubikey-sufficient

@@ -0,0 +1,2 @@
+#%PAM-1.0
+auth    sufficient      pam_yubico.so id={{ system_yubikey_id }} key={{ system_yubikey_key }}