feat: support dns-01 challenge

[yuweizzz]

support dns-01 challenge.

[fffonion]

thanks for the PR! I will do a detailed review shortly.

[fffonion]

we might want to wait the dns record to propogate after we set the record. use openresty/lua-resty-dns to query the record would be good to avoid the acme server try to validate it prematurely.

[yuweizzz]

maybe we can handle it in challenge_start_callback? I will check it.

[yuweizzz]

we still need to return a wildcard domain in domain_whitelist/domain_whitelist_callback if we quire a wildcard domain cert, do you think the new way is ok?

[fffonion]

we still need to return a wildcard domain in domain_whitelist/domain_whitelist_callback if we quire a wildcard domain cert, do you think the new way is ok?

I think you missed part of the code in commit, but I get your idea, it works for me. Basically we can do:

local WILDCARD_MATCHED = {}
function is_domain_whitelisted(domain)
  if whitelist[domain] then
    return domain
  else if regex match then
    return WILDCARD_MATCHED 
  end
  return false
end

then

local matched = is_domain_whitelisted(domain)
if matched WILDCARD_MATCHED  then
  --is wildcard match
else if matched then
  --is exact match
else
 --not match
end

[fffonion]

looks good now, some logging changes

[fffonion]

I will do a final cleanup of commits and merge to master #115

[fffonion]

Thanks for this big PR, awesome work! @yuweizzz