authelia: Install Authelia

Authelia is a general authentication provider that works (primarily)
by integrating with *nginx* using its subrequest mechanism.  It works
great with Kubernetes/*ingress-nginx* to provide authentication for
services running in the cluster, especially those that do not provide
their own authentication system.

Authelia needs a database to store session data.  It supports various
engines, but since we're only running a very small instance with no real
need for HA, SQLite on a Longhorn persistent volume is sufficient.

Configuration is done mostly through a YAML document, although some
secret values are stored in separate files, which are pointed to by
environment variables.

authelia/configuration.yml

@@ -0,0 +1,30 @@
+access_control:
+  default_policy: one_factor
+
+authentication_backend:
+  ldap:
+    base_dn: DC=pyrocufflink,DC=blue
+    implementation: activedirectory
+    tls:
+      minimum_version: TLS1.2
+    url: ldaps://pyrocufflink.blue
+    user: CN=svc.authelia,CN=Users,DC=pyrocufflink,DC=blue
+
+log:
+  level: trace
+
+notifier:
+  smtp:
+    disable_require_tls: true
+    host: mail.pyrocufflink.blue
+    port: 25
+    sender: auth@pyrocufflink.net
+
+session:
+  domain: pyrocufflink.blue
+  expiration: 1d
+  inactivity: 4h
+
+storage:
+  local:
+    path: /var/lib/authelia/db.sqlite3