OAuth 2.0 / OpenID Connect

Overview

OAuth 2.0 is the industry standard for API authorization, and OpenID Connect (OIDC) extends it for user authentication. Together they provide Authorization Code + PKCE for secure token exchange, JWT-based identity tokens, refresh token rotation, and integration with identity providers (Auth0, Okta, Keycloak, Google, Azure AD) for social login and enterprise SSO.

Instructions

• When implementing authentication, use the Authorization Code + PKCE flow for all client types (SPAs, mobile, server) since it is the only secure flow; never use the deprecated Implicit or Resource Owner Password flows.
• When validating tokens on the API side, verify the JWT signature using the provider's JWKS endpoint, check

  exp

  ,

  iss

  , and

  aud

  claims, and never trust client-side token validation alone.
• When storing tokens in web apps, use

  httpOnly

  ,

  secure

  ,

  sameSite=lax

  cookies; never store tokens in localStorage since it is vulnerable to XSS.
• When managing token lifecycle, use short-lived access tokens (5-15 minutes) with refresh token rotation where each refresh token is single-use and a new one is issued with each refresh.
• When integrating a provider, use the discovery endpoint (

  /.well-known/openid-configuration

  ) for auto-configuration rather than hardcoding endpoints.
• When implementing logout, revoke the refresh token, clear the session, and redirect to the provider's logout endpoint for complete session termination.

Examples

Example 1: Add social login to a Next.js app with PKCE

User request: "Implement Google and GitHub login for my Next.js app using OAuth 2.0"

Actions:

1. Configure the OIDC providers with client IDs and redirect URIs
2. Implement the Authorization Code + PKCE flow with state and nonce validation
3. Exchange the code for tokens and validate the ID token JWT claims
4. Store the session in httpOnly cookies with refresh token rotation

Output: A Next.js app with secure social login via Google and GitHub, PKCE-protected token exchange, and httpOnly cookie sessions.

Example 2: Secure a REST API with JWT validation

User request: "Add OAuth 2.0 token validation to my API endpoints"

Actions:

1. Fetch the provider's JWKS from the discovery endpoint
2. Create middleware that validates the access token signature, expiration, issuer, and audience
3. Extract user claims and custom scopes from the validated token
4. Return 401 for invalid tokens and 403 for insufficient scopes

Output: An API with JWT-based authorization that validates tokens against the provider's JWKS and enforces scope-based access control.

Guidelines

• Always use Authorization Code + PKCE since it is the only secure flow for all client types.
• Validate tokens on the API side: verify signature,

  exp

  ,

  iss

  , and

  aud

  ; never trust client-side validation alone.
• Use

  httpOnly

  ,

  secure

  ,

  sameSite=lax

  cookies for token storage in web apps, not localStorage.
• Implement refresh token rotation where each refresh token is single-use.
• Use the provider's discovery endpoint for configuration rather than hardcoding endpoints.
• Request minimum scopes needed:

  openid email

  for login, not all available scopes.
• Implement proper logout: revoke refresh token, clear session, redirect to provider's logout endpoint.