You can add a skipped_regex to your wordpress to let this url pass through the sso.

ynh_app_setting set wordpress skipped_regex "domain.tld/path_url"

I tried with domain.tld/.well-known and domain.tld/subdirectory/.well-known, same result :(

edit: domain.tld/.well-known redirect to the SSO, domain.tld/subdirectory/.well-known to wordpress, page not found.

You should probably replace the - by a ., that's a regex.

Anyway, I can help you using YunoHost cli command, but I can't explain you how to use that plugin.

Ok thanks.

No problem, I was thinking that yunohost SSO could have been a problem.

For the record: for nextcloud this text/html page is just a missing resource (see: YunoHost-Apps/nextcloud_ynh#198) while for wordpress it's really the SSO.
I'll check my regex, it might be wrong.

edit: I fixed the regex, same "missing resource".

Ok, I found the solution, the redirection wasn't good.

Here is the solution: change /etc/nginx/conf.d/domain.d/wordpress.conf and and this :

location /.well-known/ {
        return 301 https://$server_name/YourSubFolder/$request_uri;
}

(Automattic/wordpress-activitypub#37 (comment))

For the record, upgrading wordpress via Yunohost remove the changes in Nginx file (they are backups in /home/yunohost.conf/backup/etc/nginx/conf.d/domain.tld.conf/wordpress.conf.backupDATE).

I've seen this error again today, with Wordpress Health check saying that the WebFinger endpoint is not accessible, and it not replying with a valid JSON.
Indeed, it gets SSOed.

Adding the previously mentioned (#61 (comment)) Nginx conf lines fixed it.
I'll make a PR.