multisite – WordPress with Tor Onion Service (dual .com & .onion domains for same website)

I’d like to make my existing wordpress website www.example.com also accessible over a tor onion service = www.examplesite12345.onion. How can I do this?

Note that the two domain’s content should be identical, except that I don’t want wordpress to be injecting the wrong domain into my content (of course, all my content won’t specify the domain either).

I’m using wordpress multisite. I setup tor to point to my web server, but wordpress doesn’t recognize the domain (not surprising). So wordpress simply returns with a 302 redirect to http://www.example.com/wp-signup.php?new=www.examplesite12345.onion

How do I tell wordpress that www.examplesite12345.onion isn’t a new site, but just an alias for the existing site www.example.com? Obviously, a mere redirect from the .onion to the clearnet domain is not a valid answer.