Caddyfile

{
    on_demand_tls {
        interval 2m
        burst 10
        ask "http://localhost:33214"
    }
}

# A snippet with a couple of useful matchers
(subdomain_port) {
    map {args.0} {subdomain_port} {
        ~^([^.]+\.)?(\d+)\..+\.[^\d]+$ "${2}"
        default "0"
    }
    @reserved `{subdomain_port} in ["80", "22", "443"]`
    @valid `{subdomain_port} != "0"`
    @invalid `{subdomain_port} == "0"`
}

# Browsers start with HTTP request, so if the domain name is invalid, return an error message to avoid trying to get certificate
http:// {
    import subdomain_port {host}
    redir @valid https://{host}{uri}
    respond "Unable to find proxy port number in the domain name {host}. (Powered by @ziolko/tunnel)"
}

https:// {
    tls {
            on_demand
    }

    import subdomain_port {host}
    
    respond @reserved "Please pick another port because this one is reserved. (Powered by @ziolko/tunnel)"        
    respond @invalid "Unable to find proxy port number in the domain name {host} (Powered by @ziolko/tunnel)"
    reverse_proxy @valid localhost:{subdomain_port}

    handle_errors {
        @badGateway `{err.status_code} == 502`                
        respond @badGateway "Unable to connect to service at port {subdomain_port}. Please check if the service is running there. (Powered by @ziolko/tunnel)"               
    }
} 

# Utility endpoint to reduce number of requested certificates to domains with port in name
http://localhost:33214 {
    import subdomain_port {query.domain}
	
    respond @valid 200
    respond 400
}