skill-auth-oauth2

OAuth2 authorization code flow with PKCE requires generating a code verifier and challenge, redirecting users for consent, and exchanging the authorization code plus verifier for access tokens. This pattern secures public clients like SPAs and mobile apps without exposing client secrets.

Validating OAuth2 ID tokens using JWKS involves fetching the provider's public keys, matching the token's key ID, verifying the cryptographic signature, and checking claims like expiration and issuer. This ensures tokens are authentic and untampered.

OAuth2 token exchange supports linking user accounts across multiple providers by exchanging an incoming token for a new one representing the same subject. Backend services handle this integration to unify identities and securely manage provider-specific credentials.

PKCE and state validation for CSRF protection are needed whenever implementing OAuth2 authorization code flows, especially for public clients. State parameters bind the request to the user session, while PKCE prevents authorization code interception attacks.

Securely storing PKCE verifiers and handling client secrets server-side involves keeping secrets out of frontend code and using short-lived, session-bound storage for verifiers. This minimal secret exposure prevents interception during the OAuth2 token exchange process.