lua-resty-auto-ssl with access via proxy.

I have my servers without direct Internet access (outbound) for security reason.
I use HTTP proxy to update system packages etc.
lua-resty-auto-ssl tryting to connect to let's encrypt servers regardless of
http_proxy=http://proxy_ip:proxy_port
https_proxy=http://proxy_ip:proxy_port
ftp_proxy=http://proxy_ip:proxy_port
rsync_proxy=http://proxy_ip:proxy_port
environments from OS /etc/environment file.

Is there any way (config file or etc) I can create for lua-resty-auto-ssl to make it's work via HTTP proxy?

```
[error] 187042#187042: *42 [lua] lets_encrypt.lua:40: issue_cert(): auto-ssl: dehydrated failed: env HOOK_SECRET=xxxxx HOOK_SERVER_PORT=8999 /usr/local/bin/resty-auto-ssl/dehydrated --cron --accept-terms --no-lock --domain --challenge http-01 --config /etc/resty-auto-ssl/letsencrypt/config --hook /usr/local/bin/resty-auto-ssl/letsencrypt_hooks status: 256 out: # INFO: Using main config file /etc/resty-auto-ssl/letsencrypt/config
err: ERROR: Problem connecting to server (get for https://acme-v02.api.letsencrypt.org/directory; curl returned with 7)
, context: ssl_certificate_by_lua*, client: , server: :443
2019/10/07 16:03:58 [error] 187042#187042: *42 [lua] ssl_certificate.lua:97: issue_cert(): auto-ssl: issuing new certificate failed: dehydrated failure, context: ssl_certificate_by_lua*, client: , server: :443

```

Trace the certificate issuance path from lets_encrypt.lua:40 to the /usr/local/bin/resty-auto-ssl/dehydrated command, and inspect /etc/resty-auto-ssl/letsencrypt/config. Check how the ACME connection obtains its environment and configuration; done means certificate issuance can reach the Let's Encrypt directory through the user's HTTP proxy.

Written by the indexing model from the issue text.