httpcaddyfile: Add missing DNS challenge check for acme_dns

[rightaditya]

I was getting the following spurious error:

# cat Caddyfile
{
  acme_ca https://acme-staging-v02.api.letsencrypt.org/directory
  acme_dns cloudflare REDACTED_API_KEY
}

*.mydomain.com {
  tls {
    resolvers 1.1.1.1 1.0.0.1
  }
}
# caddy run -c Caddyfile
<snip>
Error: adapting config using caddyfile: parsing caddyfile tokens for 'tls': setting DNS challenge options [resolvers] requires a DNS provider (set with the 'dns' subdirective or 'acme_dns' global option), at Caddyfile:9

This brings the logic in line with the intended behaviour implied by the error message. (If the current behaviour is correct, then the error message should be changed accordingly.)

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[francislavoie]

Please add an adapter test to cover this case (see other .caddyfiletest files). You can use mock as the DNS provider name which is available in tests, instead of cloudflare.

[rightaditya]

@francislavoie Good point—after testing (and adding the test case), I found that the resolvers were being blown away by the presence of acme_dns. I've just updated my branch with the test and a fix for the newly-uncovered issue. PTAL.

The new issue doesn't just affect resolvers, BTW. If I have a local dns value set, acme_dns overrides it. My commit fixes that as well. I think it'd be worth adding a test for that too, but I wasn't sure about the best/preferred way to do this; AIUI, properly testing that would require a second mock provider (or allowing the mock provider to take some arguments), since they'd be indistinguishable otherwise.

[francislavoie]

Yeah makes sense re mock, go ahead and add a simple optional string field to it, useful for testing for sure.

[rightaditya]

@francislavoie Cool, just updated. Also reordered the commits to make a bit more sense. LMK if you'd prefer them squashed etc.

[francislavoie]

Commit order etc doesn't matter, we squash-merge when the PR is done

[francislavoie]

Looks perfect to me, thank you!