feature: add oidc login flow

env.example

@@ -3,9 +3,19 @@
 SKD_ALLOWED_USERS=child1,child2
 SKD_AUTH_SECRET=change-me-secret
 SKD_TOKEN_TTL_SECONDS=900
+# Auth mode: pam (default) or oidc
+SKD_AUTH_MODE=pam
 SKD_AUTH_ALLOWED_USERS=
 SKD_AUTH_ALLOWED_GROUPS=sudo
 SKD_AUTH_PAM_SERVICE=login
+SKD_OIDC_ISSUER=
+SKD_OIDC_CLIENT_ID=
+SKD_OIDC_CLIENT_SECRET=
+SKD_OIDC_REDIRECT_URI=http://localhost:8000/login/oidc/callback
+SKD_OIDC_SCOPES=openid profile email
+SKD_SESSION_COOKIE_NAME=skd_session
+SKD_SESSION_COOKIE_SECURE=false
+SKD_OIDC_STATE_COOKIE_NAME=skd_oidc_state
 SKD_DEFAULT_COUNTDOWN=60
 SKD_DEFAULT_SOUND=false
 SKD_NOTIFY_TIMEOUT=5