doc: simple reverse proxy for web browser

[coolaj86]

In order to get this working in the browser I needed a port forward proxy (from the testnet server to my desktop), and a CORS-enabled server (to allow the web browser to use the other port to access the testnet server).

# ssh -NT -L <local-port>:<target-host>:<target-port> <remote-host>
ssh -NT -L 19998:127.0.0.1:19998 my-dashd-testnet-server

# or to background it:
# ssh -nNT -L 19998:127.0.0.1:19998 my-dashd-testnet-server

/etc/hosts:

127.0.0.1   local.example.com

Caddyfile:

http://local.example.com {
    #tls internal

    log {
        output stdout
        format console
    }

    handle /* {
        root * ./
        file_server {
            browse
        }
    }
}

# CORS Preflight (OPTIONS) + Request (GET, POST, PATCH, PUT, DELETE)
(cors-api) {
    @match-cors-api-preflight {
        #not header Origin "{http.request.scheme}://{http.request.host}"
        header Origin "{http.request.header.origin}"
        method OPTIONS
    }
    handle @match-cors-api-preflight {
        header {
            Access-Control-Allow-Origin "{http.request.header.origin}"
            Access-Control-Allow-Methods "GET, POST, PUT, PATCH, DELETE, OPTIONS"
            Access-Control-Allow-Headers "Origin, Accept, Authorization, Content-Type, X-Requested-With"
            Access-Control-Allow-Credentials "true"
            Access-Control-Max-Age "3600"
            defer
        }
        respond "" 204
    }

    @match-cors-api-request {
        #not header Origin "{http.request.scheme}://{http.request.host}"
        header Origin "{http.request.header.origin}"
        not method OPTIONS
    }
    handle @match-cors-api-request {
        header {
            Access-Control-Allow-Origin "{http.request.header.origin}"
            Access-Control-Allow-Credentials "true"
            Access-Control-Max-Age "3600"
            defer
        }
    }
}

http://local.example.com:19999 {

    log {
        output stdout
        format console
    }

    handle /* {
        import cors-api
        reverse_proxy localhost:19998
    }
}