Hi,
I hit http://www.acessograduacao.ufrj.br/ and it returns the message “ACME client standalone challenge solver”.
Does anybody has an idea about it?
Thanks in advance.
Do you operate that website?
The ACME client Certbot includes a built-in web server. Usually, it only runs for a few seconds at a time, and it’s used to create certificates on computers that don’t already run web servers. (Like a mail server, for example.)
It sounds like your website is somehow running the web server from Certbot or maybe another ACME client. Maybe it was only for a few seconds? Maybe the page was cached? Maybe the subdomain is configured incorrectly?
If I access that web page, I get a 504 Gateway Timeout error from Nginx after 6 minutes.
Thanks for your reply.
I do not operate that website, I´m an user and the site may be busy or in maintenance.
Besides that, the message is curious and can´t be found on google.
Obrigado, André
I think the system administrator was trying unsuccessfully to obtain a Let’s Encrypt certificate. Hopefully the administrator will come here to the forum to ask for help with this process so that the site can support HTTPS in the future. 
Right now, the site seems to be back up again but it doesn’t have a certificate and isn’t available via HTTPS.
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