OAuth2 Client

OAuthClient.js

import fetch from 'node-fetch'

// some provider data is copied from github.com/simov/grant
const providers = {
  bogus: {
    authorize_url: "http://localhost:8282/auth/request/path",
    access_url: "http://localhost:8282/access/token/request",
  },

  google: {
    authorize_url: "https://accounts.google.com/o/oauth2/v2/auth",
    access_url: "https://oauth2.googleapis.com/token"
  },

  github: {
    authorize_url: "https://github.com/login/oauth/authorize",
    access_url: "https://github.com/login/oauth/access_token",
  },
}

export default class OAuthClient {
  constructor(config) {
    this.config = config
    this.provider = providers[config.provider]

    if (!this.provider) throw new Error(`Unknown OAuth provider ${config.provider}`)
  }

  authorizeUrl() {
    const { client_id, redirect_uri } = this.config
    const url = new URL(this.provider.authorize_url)
    const params = url.searchParams

    params.set('response_type', 'code')
    params.set('client_id', client_id)
    params.set('redirect_uri', redirect_uri)

    return url.toString()
  }

  async fetchAccessToken(code) {
    const { client_id, client_secret } = this.config

    const response = await fetch(this.provider.access_url, {
      method: 'POST',
      body: new URLSearchParams({
        grant_type: 'authorization_code',
        code,
        client_id,
        client_secret
      })
    })

    return {
      success: response.ok,
      payload: await response.json()
    }
  }
}

usage.js

import OAuthClient from './OAuthClient.js'

// instantiate the client
const client = new OAuthClient({
  provider: 'google',
  client_id: '...',
  client_secret: '...',
  redirect_uri: '...'
})

// Step 1: Generate the authorization url, and redirect the user there
const url = client.authorizationUrl()
redirectTo(url)

// Step 2: When the user returns to the callback url, the url will contain a `code` query param.
// Use that `code` to get the access token
const code = params.get('code')
const response = await client.fetchAccessToken(code)

if (response.success) {
  // log the access token
  console.log(response.payload)
}