* refactor: create log.Infof and log.Warnf
* refactor: review DNS providers.
- use one `http.Client` by provider instead of one client by request
- use the same receiver name `d` for all `DNSProvider`
- use `http.MethodXXX`
* refactor: logger init.
If Dyn responds with a 3xx or 4xx status code, information describing exactly
what went wrong is generally included in the body of the response (as part of
the typical Dyn JSON response). On the other hand, if Dyn responds with a 5xx
status code, we very likely have extremely limited information.
This commit modifies the reporting to display the explanatory messages included
in the body of the Dyn response for 3xx and 4xx status codes. The intent is to
make it much easier to determine what might be going wrong (when something is
going wrong).
Dyn provider was using incorrect zone in Present and Cleanup functions.
This uses FindZoneByFqdn() to find the correct zone for use in the
subsequent API calls.
Different DNS providers were handling credentials in different ways.
Some were reading credential environment variables in cli_handlers.go
and then passing them into the NewDNSProvider function, while others
were reading the environment variables within their NewDNSProvider
functions.
This change replaces each DNS challenge's NewDNSProvider function with
two new functions: (1) a NewDNSProvider function that takes no
parameters and uses the environment to read credentials, and (2) a
NewDNSProviderCredentials that takes credentials as parameters.
