Design OAuth 2.0 & OpenID Connect Social Login
Social Login enables users to authenticate with trusted Identity Providers (Google, GitHub, Apple) via OAuth 2.0 and OpenID Connect. It replaces password storage liability with cryptographic token verification while eliminating signup friction.
Live Architecture Studio
Edit components, modify labels, add databases, or redraw connections directly on this canvas:
1. Problem & Challenge
Users abandon apps with long registration forms and password rules. Storing passwords carries massive breach liabilities. The system must let users authenticate via external providers, exchange secure authorization codes without interception, and establish stateful or JWT app sessions.
2. Core Building Blocks & Responsibilities
👉 Swipe table horizontally to view roles and responsibilities| Component | Role | Plain-English Explanation |
|---|---|---|
| Client Web Browser | Login Initiator & PKCE Agent | Generates random PKCE code verifier and SHA-256 challenge, then redirects visitor to the identity provider. |
| Identity Provider (Google/GitHub) | Authentication Authority | Authenticates user credentials, renders the consent dialog, and issues a single-use authorization code. |
| Redirect Callback Handler | CSRF & Code Receiver | Receives the authorization code and anti-tamper state parameter from the browser redirect. |
| Backend Auth Service | Backchannel Token Exchanger | Makes a direct server-to-server POST request to the provider token endpoint using client secrets. |
| JWKS & Token Validator | Cryptographic Signature Verifier | Fetches public keys from the provider JWKS endpoint to mathematically verify RS256/ES256 signatures. |
| User Database & Session Store | Profile Upsert & Session Vault | Creates or links the local user record and issues a secure, HttpOnly session cookie. |
3. Step-by-Step Request Flow
User Clicks Social Login
Browser generates a cryptographic code_verifier, transforms it to code_challenge via SHA-256, and redirects user to IdP consent screen.
User Authenticates & Consents
Identity Provider verifies user credentials, displays requested permission scopes, and issues a 1-time Authorization Code.
Redirect to App Callback
IdP redirects browser back to application with the authorization code and state token to prevent CSRF replay.
Backchannel Code Exchange
App backend exchanges the code, client secret, and PKCE verifier directly with provider /token endpoint over TLS.
Token Issuance & Verification
IdP verifies the PKCE challenge, issues an OIDC ID Token and Access Token. Backend verifies signature via provider JWKS.
Session Established
Backend upserts user profile, creates session in Redis, and sets an encrypted HttpOnly cookie in the browser.
4. Architectural Trade-offs
Auth Code with PKCE vs Implicit Flow
Chosen: Auth Code with PKCE (RFC 7636)
Rationale: Implicit flow passes tokens in browser URL hashes where they leak into history; PKCE exchanges tokens securely via backchannel TLS.
Pure Stateless JWT vs Hybrid Server Session
Chosen: Hybrid (HttpOnly Cookie + Redis)
Rationale: Pure client-side JWTs cannot be instantly revoked upon security incidents; hybrid permits immediate session invalidation.
Interview Tip
Always explain the difference between Authentication (OpenID Connect ID Token: Who you are) and Authorization (OAuth 2.0 Access Token: What you can do). Highlighting RFC 7636 PKCE for public clients demonstrates modern security expertise.
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