🔸 TLDR
▪️ JWT = a token format (usually JSON + signature).
▪️ OAuth 2.0 = delegated authorization (“app X can access Y on my behalf”).
▪️ OpenID Connect (OIDC) = authentication layer on top of OAuth 2.0 (who you are).
▪️ SAML 2.0 = XML-based SSO standard, popular in enterprises.
👉 Modern web/mobile: OAuth2 + OIDC with JWTs. Legacy/enterprise SSO & B2B: SAML.
🔸 WHAT THEY ARE
▪️ JWT: Compact, stateless tokens (header.payload.signature) used to carry claims.
▪️ OAuth 2.0: Flows for granting scoped access (Auth Code, Client Credentials, etc.).
▪️ OIDC: Adds ID Token (often a JWT) to prove user identity.
▪️ SAML: XML assertions exchanged between IdP and SP for SSO.
🔸 WHEN TO CHOOSE WHAT
▪️ API-first / SPAs / Mobile → OAuth2 + OIDC (JWT tokens) ✅
▪️ Enterprise SSO / Older IdPs / B2B federations → SAML 🏢
▪️ Service-to-Service (no user) → OAuth2 Client Credentials 🤖
▪️ Short-lived sessions, horizontal scaling → JWT (stateless) ⚡
🔸 PROS & CONS (QUICK)
▪️ JWT: + stateless & fast; – must handle revocation/rotation, avoid long TTLs.
▪️ OAuth2/OIDC: + standardized scopes/consent; – several flows to get right.
▪️ SAML: + enterprise-ready SSO; – verbose XML, heavier tooling.
🔸 SECURITY CHECKLIST
▪️ Always verify signatures (alg, kid, issuer, audience). ✅
▪️ Prefer short-lived access tokens + refresh tokens with rotation. ⏳
▪️ HTTPS only, secure storage (no tokens in localStorage if you can avoid it). 🔒
▪️ Scopes/claims least privilege; don’t stuff sensitive data in tokens. 🧹
▪️ Key rotation (JWKS) & clock skew handling. 🔁
🔸 SPRING / JAVA HINTS
▪️ Spring Security + Spring Authorization Server / Keycloak / Auth0 integrate well.
▪️ Use Bearer tokens for APIs; validate issuer/audience and scope on each call.
▪️ Prefer opaque tokens + introspection if you need easy revocation.
🔸 TAKEAWAYS
▪️ JWT is not auth by itself; it’s a token format.
▪️ OAuth2 ≠ login; OIDC handles the login/identity part.
▪️ Pick OAuth2 + OIDC for most modern apps; SAML where enterprise SSO rules.
▪️ Security lives in the details: flows, lifetimes, rotation, validation.
#JWT #OAuth2 #OpenIDConnect #SAML #SSO #Identity #AppSec #API #Security #SpringSecurity #Java #Backend #Microservices #DevBestPractices
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