What is OAuth social login?
Social login lets users sign in with an existing account — Google, GitHub, Apple — instead of creating a new password. It uses OAuth: your app redirects the user to the provider, they approve, and the provider returns a token you exchange for the user's identity.
Why it matters
Users expect "Sign in with Google," and it removes password management from your app entirely, which is a security win. But OAuth has a precise flow with real pitfalls, so understanding it — and using a library to implement it — is the difference between smooth social login and a broken or insecure one.
What to learn
- The OAuth authorization code flow, step by step
- Providers and registering your app
- Redirect URIs and why they must be exact
- Exchanging the code for tokens server-side
- Mapping a provider identity to your user
- Linking multiple providers to one account
- Using an auth library to handle the flow
Common pitfall
Handling the token exchange on the client and exposing the client secret. The secret must stay on the server; doing the exchange in the browser leaks it and breaks the security model. Let the server (or your auth library) perform the code- for-token exchange, and never ship the client secret to the browser.
Resources
Primary (free):
- OAuth 2.0 — Official site · docs
- Auth.js — OAuth providers · docs
- Google — OAuth 2.0 · docs
Practice
Add social login with one provider using an auth library: register the app, set the redirect URI, complete the flow so a user signs in and lands authenticated, and map their provider identity to a user record. Done when sign-in works and the client secret never leaves the server.
Outcomes
- Walk through the OAuth authorization code flow.
- Configure a provider and exact redirect URIs.
- Exchange the code for tokens on the server.
- Map a provider identity to your user model.