I managed doing that by a simple qa-theme.php core hack. Not sure how to make it to a plugin:
if ((!qa_is_logged_in()) and !((strpos(qa_self_html(),'login') !== false ))) { qa_redirect('login'); }
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.