FEAT: Add Open ID Connect authentication method

* add `oidc-config` setting allowing an admin user to configure parameters
* modify login page to show another button when oidc is configured
* add dependency `openid-client` `v5.4.0`
* add backend route to process "OAuth2 Authorization Code" flow
  initialisation
* add backend route to process callback of above flow
* sign in the authenticated user with internal jwt token if internal
  user with email matching the one retrieved from oauth claims exists

Note: Only Open ID Connect Discovery is supported which most modern
Identity Providers offer.

Tested with Authentik 2023.2.2 and Keycloak 18.0.2

backend/routes/api/settings.js

@@ -69,6 +69,17 @@ router
 				});
 			})
 			.then((row) => {
+				if (row.id === 'oidc-config') {
+					// redact oidc configuration via api
+					let m = row.meta
+					row.meta = {
+						name: m.name,
+						enabled: m.enabled === true && !!(m.clientID && m.clientSecret && m.issuerURL && m.redirectURL && m.name)
+					};
+					// remove these temporary cookies used during oidc authentication
+					res.clearCookie('npm_oidc')
+					res.clearCookie('npm_oidc_error')
+				}
 				res.status(200)
 					.send(row);
 			})