README.md

lambda-edge-openid-auth

Lambda functions for authenticating against OpenID providers

Library choices

Lambda @ Edge are capped at 1048576 bytes for code so lib choice is important to minimize bundle size.

These libs are too big:

• node-jose

Usage

import { authenticateViewerRequest } from '@wanews/lambda-edge-openid-auth'
import { CloudFrontRequestHandler } from 'aws-lambda'
import pino from 'pino'

export const handler: CloudFrontRequestHandler = async (event, context) => {
  const record = event.Records[0]
  const request = record.cf.request
  const log = pino({})

  // Commit the jwks response into your repo (see below to keep updated)
  const jwks = require('../azure-login-jwks.json')

  return authenticateViewerRequest(
    {
      unauthenticatedPaths: ['/assets'],
      idps: [
        {
          clientId: '<client-id>',
          clientSecret: '<client-secret>',
          name: 'Company Azure AD',
          props: {
            type: 'azuread',
            tenantId: '<tenant-id>',
            jwks,
          },
        },
      ],
    },
    log,
    request,
  )
}

Handling key rotation

Azure AD keys can be rotated at any time, so you need to check regularly for rotation and redeploy to update the keys.

Updating keys with github actions

#.github/workflows/update-azure-jwks.yml
name: 'Update azure login JWKS'
concurrency: deployment
env:
  JWKS_PATH: path-to/azure-login-jwks.json
  # Tenant id doesn't actually matter - all the keys are the same but you need a valid one
  TENANT_ID: 'your-tenant-id'
on:
  schedule:
    - cron: '30 8 * * *'
jobs:
  redeploy-on-key-change:
    runs-on: self-hosted
    steps:
      - name: Checkout
        uses: actions/checkout@v2
        with:
          fetch-depth: 0

      - name: Fetch Azure JWKS
        run: |
          curl -o "$JWKS_PATH" "https://login.microsoftonline.com/$TENANT_ID/discovery/keys"
          git config user.email "[email protected]"
          git config user.name "SWM GitHub Service Account"
          git add "$JWKS_PATH"
          git commit -m "Update azure login JWKS" || echo "No changes to commit"
          git pull --rebase
          git push