Is it possible to generate a cert for a subdomain with no DNS record?

I have set up a subdomain in order to run phpMyAdmin. Our intention was to not have an A record for this subdomain, with the two people who need to access it configuring their HOSTS files. (which I guess counts as security by obfuscation).

However, Certbot refused to create the cert:

Failed authorization procedure. (http-01): urn:acme:error:unknownHost :: The server could not resolve a domain name :: No valid IP addresses found for

 - The following errors were reported by the server:
   Type:   unknownHost
   Detail: No valid IP addresses found for

Now I could create the A record and remove it after generating the certificate, but this is a nuisance, and wouldn't I have to repeat it every 90 days to renew the cert (worse, would it affect the auto-renew of the other subdomain certs?)
Is there any alternative workaround?

My operating system is (include version): CentOS 6.8

My web server is (include version): Apache 2.4

I can login to a root shell on my machine (yes or no, or I don't know): yes

I'm using a control panel to manage my site (no, or provide the name and version of the control panel): no

Use dns-01 challenge?

There doesn’t have to be an A or AAAA record but the name must exist in DNS. You can prove control with a DNS TXT record (thus Let’s Encrypt don’t actually connect to the machine)

If you control the domain but aren’t willing to have any records for the exact name, other CAs may be able to accommodate that but Let’s Encrypt does not.

Also keep in mind that Let’s Encrypt publishes all the certificates it signs to the Certificate Transparency logs. Some CAs today don’t do that, or will let you opt out, but certificates are public documents and anybody who sees a certificate is entitled to add it to a log. It is very possible that key trust stores will make this mandatory at some point to protect the integrity of the PKI. So you probably shouldn’t aim to keep the contents of the certificate secret.

How do I go about this? I presume that the TXT record will have to be a string that Lets Encrypt provides?

The latest versions of Certbot or some other Let’s Encrypt clients, particularly those using bash for some reason offer to prove control through dns-01 challenges. This challenge type is the one with TXT records. You should read documentation specific to the client you’ll use. Ideally you have some way for a program to update DNS as doing it by hand several times per year will get old.

hi dramatic

have a look at clients such as certbot or bash

Most DNS providers also have an API interface for updating txt records which you can use to help with automation

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