chore: update google credentials instructions

docs/content/docs/authentication/google.mdx

@@ -9,6 +9,22 @@ description: Google provider setup and usage.
         To use Google as a social provider, you need to get your Google credentials. You can get them by creating a new project in the [Google Cloud Console](https://console.cloud.google.com/apis/dashboard).
 
         In the Google Cloud Console > Credentials > Authorized redirect URIs, make sure to set the redirect URL to `http://localhost:3000/api/auth/callback/google` for local development. For production, make sure to set the redirect URL as your application domain, e.g. `https://example.com/api/auth/callback/google`. If you change the base path of the auth routes, you should update the redirect URL accordingly.
+
+        <Callout type="info">
+        **Creating Your Google OAuth Credentials**
+
+        If you haven't created OAuth credentials yet, follow these step-by-step instructions:
+
+        1. Open **Google Cloud Console** → **APIs & Services** → **Credentials**
+        2. Click **Create Credentials** → **OAuth client ID**
+        3. Choose **Web application**
+        4. Add your redirect URIs:
+           - `http://localhost:3000/api/auth/callback/google` (for local development)
+           - `https://your-domain.com/api/auth/callback/google` (for production)
+        5. Copy the **Client ID** and **Client Secret** into your environment variables
+
+        These steps avoid common issues such as `redirect_uri_mismatch`.
+        </Callout>
     </Step>
 
   <Step>