OAuth: Support standard authentication with short-living password received with OIDC token (#9530)

config/defaults.inc.php

@@ -411,6 +411,13 @@ $config['oauth_user_create_map'] = [
     'language' => ['locale'],
 ];
 
+// Optional: For backends that don't support XOAUTH2/OAUTHBEARER method we can still use
+// OpenIDC protocol to get a short-living password (claim) for the user to log into IMAP/SMTP.
+// That password have to have (at least) the same expiration time as the token, and will be
+// renewed on token refresh.
+// Note: The claim have to be added to 'oauth_scope' above.
+$config['oauth_password_claim'] = null;
+
 // /// Example config for Gmail
 
 // Register your service at https://console.developers.google.com/