dns challenge feature with support for external dns tools like the dehydrated project

[mscalora]

Lukas Schauer's dehydrated has support for external dns tools to enable "ACME DNS challenge" for the many situations where http challenge is problematic. Generally it just runs a command with parameters specifying the FQDN and magic value that need to be setup as a TXT dns record and then a cleanup after letsencrypt is done verifying. It would be super-cool you used the same 'protocol' so that existing tools work out-of-the-box. See: https://github.com/lukas2511/dehydrated/blob/master/docs/dns-verification.md

dehydrated works but since it is written in BASH is sensitive to many platform issues and has a lot of dependencies on various unix/linux tools.