How to execute PHP from the ffl-template.tpl file

Hi support,

I would like to be able to output some php code in my custom pop-up login template underneath the login form. I have the custom template setup at:
/wp-content/themes/[my-child-theme]/flexible-frontend-login/ffl-template.tpl

All I need to do is execute this code underneath the ffl-form-table:
<?php do_action('oa_social_login'); ?>

When this works it will output social login buttons that work with the oneall social login plugin:
https://www.ads-software.com/plugins/oa-social-login/

My question is how can I achieve this? {php} and {include_php} tags are deprecated in the smarty template engine. So smarty recommends creating a plugin to execute the code. Could you give me some guidance on how to achieve this?

Thanks,
Mike S