1.0.0 • Public • Published

Curveball browser-to-bearer

This package contains a Curveball middleware that allows a user with a regular browser to log into an API that's an OAuth2 resource server.

It will do so by intercepting HTTP 401 Unauthorized errors, seeing if the user wanted Accept: text/html and redirect the user to an OAuth2 authorization endpoint.

After the user comes back, the access token gets validated and placed into a cookie. This cookie is then converted to an Authorization header, which will make it seem to the resource server that the user has normal OAuth2 authorization information.

What this enables in a nutshell is allowing developers to browse OAuth2 APIs with a browser, which otherwise is pretty hard to do.


npm install @curveball/browser-to-bearer @curveball/oauth2@0.3 @badgateway/oauth2-client

The @curveball/oauth2 curveball middleware is not required. If you have a custom middleware that listens for a Authorization: Bearer HTTP header, this should also work.

The examples below assume you use the @curveball/oauth2 middleware though.

Getting started

This middleware needs to be loaded before your normal authorization middelware to work correctly. In theory this middleware can work with any OAuth2 middleware, but the below example is using the @curveball/oauth2 middleware.

In addition to a working OAuth2 middleware, it also requires a session middleware.

import { Application } from '@curveball/core';
import oauth2 from '@curveball/oauth2';
import browserToBearer from '@curveball/browser-to-bearer';
import session from '@curveball/session';
import { OAuth2Client } from '@badgateway/oauth2-client';

const app = new Application();

const client = OAuth2Client({

  server: 'https://auth.example/',
  clientId: 'My-app',
  clientSecret: 'some_client_secret',

   * Only specify these if your OAuth2 server _doesn't_ support auto
   * discovery of these endpoints.
   * If your server does support auto-discovery (through the OAuth2
   * Authorization Metadata document), it's better to omit these as
   * it will future-proof your code.
  authorizationEndpoint: '/authorize',
  tokenEndpoint: '/token',
  introspectionEndpoint: '/introspect',


  store: 'memory',
  cookieOptions: {
    httpOnly: true,
    // It might be important to set sameSite to false to allow this to work.
    // Without this, cookies will not be sent along after the first redirect
    // from the OAuth2 server.
    sameSite: false,



Setting the right origin

By default Curveball will assume you are running this package on http://localhost, which breaks the redirect back from the authentication server to your app.

To fix this, either:

  1. Set the CURVEBALL_ORIGIN environment variable. This is recommended in most modern deployments. It should have a value such as https://domain.example without any slashes in the end.
  2. Set app.origin = 'https://domain.example. This is done on the main Curveball application object.

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npm i @curveball/browser-to-bearer

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