Demystifying OAuth Security: State vs. Nonce vs. PKCE

OAuth 2.0 and OpenID Connect use three distinct security parameters that work together but serve different purposes. The state parameter prevents CSRF attacks by validating that authorization responses match the original request. The nonce parameter prevents ID token replay attacks by cryptographically binding tokens to specific client sessions. PKCE (Proof Key for Code Exchange) prevents authorization code interception by requiring clients to prove they initiated the flow. These mechanisms create layered security protecting different stages of the authentication process, and all three should be implemented together rather than treating them as interchangeable alternatives.