Google OAuth Login
Overview
Streamlined authentication flow using Google OAuth 2.0, allowing users to sign in with their existing Google accounts. The system handles account creation, linking, and session management while maintaining security best practices.
User Stories
- As a user, I want to sign in with my Google account, so that I don't need to create another password
- As a user, I want my profile information auto-filled from Google, so that I save time during signup
- As a new user, I want my account automatically created on first login, so that the process is seamless
- As an existing user, I want to link my Google account to my email/password account, so that I have multiple login options
Acceptance Criteria
- [ ] "Sign in with Google" button is prominent on login page
- [ ] Clicking button redirects to Google OAuth consent screen
- [ ] User can approve or deny permission requests
- [ ] System creates new account if email doesn't exist
- [ ] System links to existing account if email matches
- [ ] Profile data (name, email, avatar) is synced from Google
- [ ] User is redirected to intended page after successful login
- [ ] Error handling for declined permissions or OAuth failures
Technical Requirements
- Register application in Google Cloud Console
- Implement OAuth 2.0 authorization code flow
- Request minimal scopes (profile, email)
- Validate OAuth state parameter to prevent CSRF
- Verify Google ID tokens on backend
- Store OAuth tokens securely if needed for API access
- Handle token refresh for long-lived sessions
Edge Cases
- User cancels Google login → Redirect back to login page with no error
- Google account email already exists in system → Auto-link accounts if email verified
- User revokes Google app permissions → Detect on next login and re-request consent
- Multiple Google accounts logged in browser → User can select which account to use
- OAuth callback fails or times out → Show error with retry option
Out of Scope
- Other OAuth providers (Facebook, GitHub, Apple)
- Google One Tap login
- Google Smart Lock integration
- Syncing calendar or Gmail data