This server exchanges a Snapchat OAuth authorization code for a Firebase custom token so the React app can sign in with signInWithCustomToken.

1. Copy .env.example to .env.
2. In the Snapchat Developer Portal, create an app. For this server-side flow use the Confidential OAuth 2.0 Client ID and its Client Secret. Under Login Kit, add a redirect URI:
   • Dev: http://localhost:5173/auth/snapchat/callback
   • Production: https://your-domain.com/auth/snapchat/callback
3. In .env, set SNAPCHAT_CLIENT_ID (use the Confidential OAuth 2.0 Client ID from the portal) and SNAPCHAT_CLIENT_SECRET.
4. For Firebase Admin, either:
   • Set FIREBASE_SERVICE_ACCOUNT_PATH to the path to your service account JSON (e.g. ./serviceAccountKey.json), or
   • Set GOOGLE_APPLICATION_CREDENTIALS to that path and leave FIREBASE_SERVICE_ACCOUNT_PATH unset.

pnpm install
pnpm run build
pnpm start

For development with auto-restart:

pnpm run dev

Server listens on http://localhost:4000 by default. The React example uses VITE_CUSTOM_AUTH_SERVER_URL=http://localhost:4000 (default) so the Snapchat button and callback can reach it.

• GET /auth/snapchat/config – returns clientId, authUrl, and scopes for the client to start the OAuth redirect.
• POST /auth/snapchat/token – body { code, redirect_uri }; exchanges with Snapchat, fetches user id, mints a Firebase custom token; returns { customToken }.