I think you can user OAuth2.0 client plugin for Wordpress to make users to login to your Woordpress site with your UNA site login, for example you can use plugin like this:

https://wordpress.org/plugins/oauth-client/

To configure it you need to generate key&secret pair for your Wordpress site (make sure you specified correct Wordpress site URL) and configure the following UNA OAuth2 endpoints:

Authorize endpoint: http://your-una.site/m/oauth2/token
Access token endpoint: http://your-una.site/m/oauth2/auth
Identity endpoint: http://your-una.site/m/oauth2/api/me
Scope: basic
Attributes: id, email, picture, profile_link, name or profile_display_name