Using nfqueue on Linux as a novel, webserver-agnostic HTTP authenticator

[jvanasco]

@_az

I'd be curious to hear what other client authors on Linux think. My feeling for a long time has been that fulfilling ACME challenges often requires an outsized effort to "make it work" and it'd be nice to find further ways to reduce friction on the sysadmin side.

I absolutely love this, and it solves a lot of the issues I was talking about in Http challange on port 25? - #20 by webprofusion without having to create a new challenge type. I still think a new challenge type is needed, but this would address a very large amount of the use cases.