NGINX SXG extension

Signed HTTP Exchange (SXG) support for nginx. Nginx will convert responses from the upstream application into SXG when client requests include the Accept: application/signed-exchane;v=b3 HTTP header with highest qvalue.

Installation

There are two options for installation: Debian package or build from source. See this article for more details.

Configuration

Nginx-SXG module requires configuration on nginx.

Directives

sxg

Activation flag of SXG module.

• on: Enable this plugin.
• off: Disable this plugin.

Default value is off.

sxg_certificate

Full path for the certificate file. The certificate requires all of the conditions below to match.

• Has CanSignHttpExchanges extension.
• Uses ECDSA256 or ECDSA384.

This directive is always required.

sxg_certificate_key

Full path for the private key for the certificate.

This directive is always required.

sxg_cert_url

URL for CBOR encoded certificate file. The protocol must be https.

This directive is always required.

sxg_validity_url

URL for the validity information file. It must be https and must be the same origin with the website.

This directive is always required.

sxg_max_payload

Maximum HTTP body size this module can generate SXG from. Default value is 67108864 (64 MiB).

sxg_cert_path

An absolute path in which nginx will generate and serve the CBOR-encoded certificate file. But make sure that the OCSP responder for the certificate is accessible from your nginx server to get OCSP responses. This directive is optional.

sxg_expiry_seconds

The life-span of generated SXG file in seconds. It must not be bigger than 604800 (1 week). This directive is optional. The default value is 86400 (1 day).

Config Example

load_module "modules/ngx_http_sxg_filter_module.so";

http {
    upstream app {
        server 127.0.0.1:3000;
    }
    include       mime.types;
    default_type  application/octet-stream;
    subrequest_output_buffer_size   4096k;

    server {
        listen    80;
        server_name  example.com;

        sxg on;
        sxg_certificate     /path/to/certificate-ecdsa.pem;
        sxg_certificate_key /path/to/private-key-ecdsa.key;
        sxg_cert_url        https://cdn.test.com/example.com.cert.cbor;
        sxg_validity_url    https://example.com/validity/resource.msg;
        sxg_expires_seconds 604800;

        location / {
            proxy_pass http://app;
        }
    }
}

Subresource support

nginx-sxg-module automatically includes signatures of subresources in its responses, allowing end users to prefetch it from distributor. When finding link: rel="preload" entry in HTTP response header from upstream, this plugin will collect the specified resource to the upstream and append rel="allowed-alt-sxg";header-integrity="sha256-...." to the original HTTP response automatically. This functionality is essential to subresource preloading for faster cross-site navigation.