Fixing The Certbot Issue “The client lacks sufficient authorization/404 Not Found…”

I am a huge fan of Let’s Encrypt and their free SSL certificate service using Certbot. However, recently whilst setting up a new domain name and attempting to get a certificate, I encountered an error I had never experienced before.

The client lacks sufficient authorization :: The key authorization file from the server did not match this challenge

It couldn’t access the folder where it stored the secrets and was resulting in a 404 error. I manually created the folder and I could access it, so why Certbot couldn’t was a mystery.

After some investigation and dead-end Googling, I found the problem and fixed it. I use Linode for my hosting and use the default DNS entries option when adding a new domain.

Well, it turns out by default Linode will add IPv6 AAAA entries to the server and if you do not have Nginx configured to handle IPv6, it will not resolve properly.

It looked something like this:

The culprit was the second entry for the domain with the weird value 2400:8902::f03c:91ff:fe59:f74c this is an IPv6 address and unless you have your server configured to support them, it’ll result in an error when trying to create an SSL certificate.

The fix ends up being rather simple. Either update your server to support those types of addresses or remove the IPV6 entries from your DNS settings and make sure you wait a good 10-20 minutes before trying again.

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