Generating JWT token [http/authorization/gen_hs_jwt]

This example will construct a JSON Web Token (JWT) from scratch including generating the digital signature.

Step 1: Use the following commands to start your NGINX container with this lab’s files: Notice the JWT_GEN_KEY environment variable

EXAMPLE='http/authorization/gen_hs_jwt'
docker run --rm --name njs_example -e JWT_GEN_KEY="foo" -v $(pwd)/conf/$EXAMPLE.conf:/etc/nginx/nginx.conf:ro -v $(pwd)/njs/:/etc/nginx/njs/:ro -p 80:80 -d nginx

Step 2: Now let’s use curl to test our NGINX server:

curl 'http://localhost/jwt'
eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiIsImV4cCI6MTU4NDcyMjk2MH0.eyJpc3MiOiJuZ2lueCIsInN1YiI6ImFsaWNlIiwiZm9vIjoxMjMsImJhciI6InFxIiwienl4IjpmYWxzZX0.GxfKkJSWI4oq5sGBg4aKRAcFeKmiA6v4TR43HbcP2X8

docker stop njs_example

Code Snippets

This config uses js_set to invoke the jwt function in our njs code. The generated JWT is returned in the response body.

nginx.conf

env JWT_GEN_KEY;

...

http {
  js_path "/etc/nginx/njs/";

  js_import utils.js;
  js_import main from http/authorization/gen_hs_jwt.js;

  js_set $jwt main.jwt;

  server {
...
      location /jwt {
          return 200 $jwt;
      }
  }
}

The njs code creates a claims object and then builds the JWT by combining the header, claims, and a digital signature.

gen_hs_jwt.js

  function generate_hs256_jwt(claims, key, valid) {
      var header = { typ: "JWT",  alg: "HS256" };
      var claims = Object.assign(claims, {exp: Math.floor(Date.now()/1000) + valid});

      var s = [header, claims].map(JSON.stringify)
                              .map(v=>v.toString('base64url'))
                              .join('.');

      var h = require('crypto').createHmac('sha256', key);

      return s + '.' + h.update(s).digest().toString('base64url');
  }

  function jwt(r) {
      var claims = {
          iss: "nginx",
          sub: "alice",
          foo: 123,
          bar: "qq",
          zyx: false
      };

      return generate_hs256_jwt(claims, process.env.JWT_GEN_KEY, 600);
  }

  export default {jwt}