Google Login, explained.

How "Sign in with Google" works with Better-Auth. Four steps, three lines of code.

The flow

What happens when a user clicks "Mit Google anmelden"

1. User clicks the Google button

On your sign-in page. Your SPA calls signIn.social({ provider: "google" })

2. Browser redirects to Google

Google shows their OAuth consent screen. User picks their Google account and clicks "Allow".

3. Google redirects back to your auth-server

Hits /api/auth/callback/google. Better-Auth verifies the token with Google, gets the user's name + email.

4. Better-Auth creates user + session

Inserts into user + account (provider: google) + session. Sets the session cookie.

5. User lands back on your site, logged in

Redirected to /. Header shows their Google name. No password needed.

Your sign-in page

What the user sees

sitzio.de/sign-in

Google's screen

What Google shows

accounts.google.com

Automatic

What Better-Auth handles for you

👤

New user

First Google login → creates user + account (google) + session

🔗

Same email exists

Already signed up with email+password? Google account links to existing user automatically.

🔄

Returning user

Already has Google account linked → just creates new session. Instant login.

Implementation

Three lines of code

auth-server/src/auth.ts Server

// Add to betterAuth({ ... }):

socialProviders: {
  google: {
    clientId: process.env.GOOGLE_CLIENT_ID,
    clientSecret: process.env.GOOGLE_CLIENT_SECRET,
  },
},

src/pages/SignInPage.tsx Client

// The Google button calls:

authClient.signIn.social({
  provider: "google",
  callbackURL: "/",
})

That's it. Better-Auth handles the OAuth flow, token exchange, user creation, account linking, and session management. You write the config + one button click handler.

Setup

Four steps to enable it

Step 1 — Google Cloud

Create OAuth credentials

Google Cloud Console → APIs & Services → Credentials → Create OAuth 2.0 Client ID. Copy Client ID + Client Secret.

Step 2 — Redirect URI

Add callback URL

In Google's OAuth settings, add:
http://localhost:3001/api/auth/callback/google (dev)
https://sitzio.de/api/auth/callback/google (prod)

Step 3 — Backend

Add to auth.ts

Add socialProviders.google with the client ID and secret. Set them as env vars, not hardcoded.

Step 4 — Frontend

Add the button

Add "Mit Google anmelden" button on the sign-in page. One click handler: signIn.social({ provider: "google" })

At 50 sites

How it scales

One Google Cloud project works for all sites. Add each site's callback URL to the same OAuth credential. Each site's auth-server uses the same client ID + secret. Or create one credential per site if you want full isolation. Google doesn't charge for OAuth — it's free at any scale.