You’re just getting an HTTP->HTTPS redirect here. There’s no problem there.
This looks suspicious though. What’s openresty? Seems like it’s causing the redirect.
I don’t think you need any of these lines. Caddy already sets the appropriate headers.
I don’t recommend using a subpath for proxying services like this; they typically need specific support for being run under a subpath. It’s better to use a subdomain for each service. See this article for details: