Memcached http provider

Publishes challenges into memcached where they can be retrieved by nginx. Allows specifying multiple memcached servers and the responses will be published to all of them, making it easier to verify when your domain is hosted on a cluster of servers.

Example nginx config:

    location /.well-known/acme-challenge/ {
        set $memcached_key "$uri";
        memcached_pass 127.0.0.1:11211;
    }