Version: 5.1.2 Problem: Current DoH server (based on lua-http) is slow and very hard to debug (e.g. #465). Proposed approach: Complete rewrite using a better HTTP library. Considerations: - [x] drop HTTP1 support, https://tools.ietf.org/html/rfc8484 recommends HTTP2 anyway: > HTTP/2 [RFC7540] is the minimum RECOMMENDED version of HTTP for use with DoH - [x] drop support for insecure transport (HTTP-only): Insecure transport complicates design and implementation and has unclear benefits. Let's not implement it before there is clear use-case for it. - [x] ~~design a extensibility mechanism for kresd modules [#616]~~