resty.auto-ssl.storage_adapters.redis

I'm trying to use the storage adapter for Redis but I can't get connect to an external Redis server which can be connected from the instance where is openresty using redis-cli but doesn't work, then I installed a Redis Server in the same machine without authentication but this does't still work.

This is code

```
init_by_lua_block {
auto_ssl = (require "resty.auto-ssl").new()
auto_ssl:set("storage_adapter", "resty.auto-ssl.storage_adapters.redis")
auto_ssl:set("redis", {socket = "unix:/var/run/redis/redis.sock"})
auto_ssl:set("allow_domain", function(domain)
return true
end)
auto_ssl:init()
}
```

I get this error

`auto-ssl: could not get certificate for sub.hostname.com - using fallback - failed to get or issue certificate, context: ssl_certificate_by_lua*`

Start by reading the resty.auto-ssl.storage_adapters.redis adapter and reproducing the init_by_lua_block configuration with the Unix socket at /var/run/redis/redis.sock. Compare the adapter's connection expectations with the reported ssl_certificate_by_lua* error; done means the configured Redis server can be used to retrieve or issue the certificate instead of falling back.

Written by the indexing model from the issue text.