[FEAT]: DNS should be selectable

[Zottelchen]

What happened?

Just started out with Cosmos, I like the onboarding. I set up the DNS challenge for Cloudflare + Wildcard certificate.

But then comes the issue. I want to use Cosmos in a private network. Additionally the private network is forced to use NextDNS. I think this causes some problems with DNS-Lookup/DNSSEC (most likely because of CNAME Flattening).

What should have happened?

Add an additional field for a DNS which is used for the LetsEncrypt lookups only. Caddy does something similiar with 'resolvers' in the tls directive.

How to reproduce the bug?

1. Onboard in a private Network which forces NextDNS + CNAME Flattening
2. DNSSEC fails
3. No Certificates

Relevant log output

2023/07/08 03:05:47 [ERROR] LETSENCRYPT_OBTAIN : error: one or more domains had a problem:
[schmu.li] acme: error: 400 :: urn:ietf:params:acme:error:dns :: DNS problem: looking up A for <DOMAIN>: DNSSEC: RRSIGs Missing; DNS problem: looking up AAAA for <DOMAIN>: DNSSEC: RRSIGs Missing

2023/07/08 03:05:47 [ERROR] Getting TLS certificate. Fallback to SELFSIGNED certificates :

Other details

No response

System details

Cosmos:latest

[paulhugill]

Is there any plans to implement this (or something else) to solve the issue of split brain DNS?

This seems like it would be a useful feature for a number of people.
Either the closed PR on this, or the currently open one should probably work for most of us.

---

Edit: Finally found the setting to be able to do this, seems like it was added in v0.16.1 but I can't find any documentation about using it or even using the config file.

For anyone that needs it, you can edit the HTTPConfig.DnsChallengeResolvers in the cosmos.config.json file.
In mine, I think I have the defaults, so location is at /var/lib/cosmos.
I believe the format is just comma separated string "server1,server2" but I only put one.

Hope that helps anyone else in this situation.