Discord OAuth protected endpoints with only nginx

conf.d~auth.conf

js_include conf.d/oauth2.js;

server {
  listen 80;
  server_name localhost;
  root /usr/share/nginx/html;

  location / {
    auth_request /_auth_init;
  }

  location = /_auth_init {
    set $access_token "";
    internal;
    js_content fromCode;
  }

  location /_auth {
    internal;
    gunzip on;
    proxy_method POST;
    proxy_set_header Content-Type "application/x-www-form-urlencoded";
    proxy_pass https://discordapp.com/api/oauth2/token;
  }

  location /_me {
    internal;
    gunzip on;
    proxy_method GET;
    proxy_set_header Authorization "Bearer $access_token";
    proxy_pass https://discordapp.com/api/users/@me;
  }
}

conf.d~oauth2.js

// Discord application credentials
var CLIENT_ID = 'client id';
var CLIENT_SECRET = 'client secret';

// Base URL of the protected routes
var BASE_URL = 'http://localhost';

// A whitelist of Discord user IDs you wanna whitelist
var whitelist = [
  '107217872262017024' // Paturages
];

function fromCode(r) {
  function me(reply) {
    if (reply.status == 200) {
      var response = JSON.parse(reply.responseBody);
      if (whitelist.indexOf(response.id) > -1) {
        r.return(204);
      } else {
        r.return(403);
      }
    } else {
      r.return(401);
    }
  }

  function auth(reply) {
    if (reply.status == 200) {
      var response = JSON.parse(reply.responseBody);
      // Set the variable for /_me
      r.variables.access_token = response.access_token;
      r.subrequest('/_me', me);
    } else {
      r.return(401);
    }
  }

  var code = r.variables.request_uri.split('=')[1];
  var path = r.variables.request_uri.split('?')[0];
  r.subrequest(
    '/_auth',
    {
      method: 'POST',
      body:
        'client_id=' + CLIENT_ID +
        '&client_secret=' + CLIENT_SECRET +
        '&grant_type=authorization_code' +
        '&code=' + code +
        '&redirect_uri=' + BASE_URL + path +
        '&scope=identify'
    },
    auth
  );
}

nginx.conf

user nginx;
worker_processes 1;

# Load the dynamic NJS module
load_module modules/ngx_http_js_module.so;
load_module modules/ngx_stream_js_module.so;

events {
  worker_connections 1024;
}

http {
  include /etc/nginx/conf.d/*.conf;
}