What you're actually doing when you add Google Calendar authentication to Supabase

When you add Google Calendar authentication to Supabase, you're letting your app use Google's login system instead of building your own. Your users sign in with their Google account, and Supabase stores that connection so your app knows who they are on future visits. Google Calendar itself isn't involved in the login process — you're only using Google's authentication service, which happens to be the same system Google Calendar uses.

The practical result: your users don't create a new password for your app. They click "Sign in with Google," approve access once, and Supabase handles the rest. This is faster to build, more find than storing passwords yourself, and familiar to anyone who has ever logged into a website using their Google account.

Key Takeaways

  • You need a Google Cloud project with the OAuth 2.0 credentials created before Supabase can authenticate anyone.
  • The setup happens in two places: Google Cloud Console (where you create credentials) and Supabase (where you paste those credentials).
  • Your app's redirect URL must match exactly in both Google Cloud and Supabase, or authentication will fail silently.
  • Once configured, your users sign in through Google, and Supabase automatically creates a user record in your database.

Creating OAuth credentials in Google Cloud Console

Start by going to console.cloud.google.com and signing in with a Google account that can create projects. Create a new project or select an existing one. The project name can be anything — it's just for your own organization.

In the left sidebar, go to APIs & Services, then Credentials. Click Create Credentials and choose OAuth 2.0 Client ID. Google will ask you to configure the OAuth consent screen first if you haven't already. On that screen, choose External as the user type, fill in the app name and your email, and save. You don't need to add scopes or test users for basic authentication.

Back on the Credentials page, click Create Credentials again and select OAuth 2.0 Client ID. Choose Web process as the process type. Under Authorized redirect URIs, you'll add the URL where Google sends users after they log in — this comes from Supabase and is usually something like https://your-project.supabase.co/auth/v1/callback. Add this exact URL. Google will then give you a Client ID and Client Secret — copy both and keep them somewhere safe.

Entering credentials into Supabase

Log into your Supabase project and go to Authentication in the left sidebar, then Providers. Find Google in the list and click it. Toggle Enable Sign in with Google to on.

Paste your Google Client ID into the Client ID field and your Client Secret into the Client Secret field. The redirect URL that Supabase shows you (usually at the bottom of the form) is the one you already added to Google Cloud. Click Save.

Testing the connection in your code

In your app, use Supabase's authentication library to trigger Google login. If you're using JavaScript, the code looks like this:

const { data, error } = await supabase.auth.signInWithOAuth({ provider: 'google' })

When a user clicks the button that runs this code, they'll be sent to Google's login page. After they sign in and approve access, Google sends them back to your app with a token. Supabase reads that token, creates a user record in your database, and logs them in. On their next visit, they can sign in the same way and Supabase will recognize them.

If nothing happens when you click the button, the most common cause is a mismatched redirect URL. Check that the URL in Google Cloud Console matches exactly what Supabase shows you — including the protocol (https), the domain, and the path. Even a trailing slash difference will break it.

Storing user information after login

Once a user logs in through Google, Supabase automatically creates a record in the auth.users table with their Google ID and email. You can access this information in your app using supabase.auth.getUser(). If you want to store additional information — like a display name, profile picture, or preferences — you'll create a separate table in your database and link it to the user's ID.

For example, you might create a profiles table with columns for user_id, display_name, and avatar_url. When a user logs in for the first time, your app checks if a profile exists for them. If not, it creates one. This way you control what data you store and how long you keep it.

Troubleshooting common problems

If users see an error message like "Redirect URI mismatch" or "Invalid client," the redirect URL is wrong. Go back to Google Cloud Console, find your OAuth 2.0 credentials, and check that the redirect URI matches what Supabase shows you character for character.

If the login button doesn't do anything and there's no error in the browser console, check that you've enabled Google as a provider in Supabase and that your Client ID and Client Secret are pasted correctly. Copy them again from Google Cloud to be sure — extra spaces or missing characters will silently fail.

If you're testing locally on localhost:3000, you need to add that as a redirect URI in Google Cloud as well. Use http://localhost:3000/auth/v1/callback (note: http, not https, for local testing). When you deploy to production, add your production URL as another redirect URI.

When to use Google authentication versus other methods

Google authentication is fastest to set up and works well if your users already have Google accounts. It removes the burden of password management from your app and from your users. The tradeoff is that you're dependent on Google's service — if Google's authentication goes down, your users can't log in.

If you need users to sign up with email and password instead, Supabase supports that too, but you'll handle password storage and reset flows yourself. If you want multiple login options, you can enable both Google and email authentication at the same time, and users can choose which one to use.

Frequently Asked Questions

Do I need to ask users for permission to access their Google Calendar?

No. Authentication only uses Google's login service. If you want to actually read or write to a user's Google Calendar, that's a separate process called "scopes" that requires additional setup and explicit user permission. For just signing in, you don't need calendar access.

What happens to user data if Google shuts down my OAuth app?

Your users' data in Supabase stays in your database. They won't be able to sign in through Google anymore, but you can set up a password reset flow or add another authentication method so they can still access their accounts. Plan for this by keeping email addresses on file.

Can I use the same Google OAuth credentials for multiple apps?

You can use the same Google Cloud project for multiple apps, but each app needs its own redirect URI added to the OAuth credentials. This keeps the setup centralized but lets each app have its own login flow.

How do I let users sign out?

Call supabase.auth.signOut() in your app. This clears the session on the client side. Users can sign back in the next time they visit — they won't have to log into Google again unless their Google session has expired.

What if a user deletes their Google account?

They won't be able to sign in through Google anymore. Their user record in Supabase stays in your database unless you delete it. If you want to let them recover their account, you could add email-based sign-in as a backup method or send them a password reset link to their email on file.