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🧩 JWT vs OIDC — Separate but Together

1. JWT (JSON Web Token)

• What it is: A token format (just a container for claims).
• What it looks like: header.payload.signature
• Who uses it: Both humans and services.
• What it carries: Facts like:
  • sub → who the token is about
  • aud → who the token is for
  • exp → when it expires

👉 JWT is like a passport card — it holds information and a signature that proves authenticity.

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2. OIDC (OpenID Connect)

• What it is: A protocol (set of rules) built on top of OAuth2.
• Purpose: To let apps log users in and know who they are.
• What it gives you:
  • ID Token → usually a JWT that says “This user is Alice, verified by Google/Okta/etc.”
  • Access Token → used to call APIs (sometimes also a JWT).

👉 OIDC is like the border control process — the steps (passport check, stamps) that result in you getting that passport card (JWT) to travel with.

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3. How they fit together

• JWT = the format
• OIDC = the login protocol that issues JWTs

So:

• A user logs in via OIDC.
• The IdP (e.g., Google, Okta, Cognito) hands back an ID Token, which is a JWT.
• Your app or API validates the JWT.

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4. Use cases side by side

Situation	What you use	Example
Human login	OIDC → issues JWT (ID Token)	User signs in with Google → app gets ID Token JWT
Service calling service	JWT directly (OAuth2 Client Credentials)	Microservice A calls Microservice B using JWT access token
API Gateway	Validates JWTs (from OIDC or service flows)	AWS API Gateway checks JWT from Cognito or Firebase

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5. 🔑 Key takeaway

• JWT is a token format.
• OIDC is a login protocol.
• OIDC tokens are JWTs.
• For users → OIDC (login flow) → JWTs.
• For services → JWTs (via OAuth2 or workload identity).

So yes — separate (format vs protocol), but always together in practice.

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JWT & OIDC — The Plain-English Guide (from Fundamentals to Advanced)

0) The 1-minute mental model

• JWT = a sealed card (digitally signed) that carries facts (“who/what/when/permissions”). Anyone with the issuer’s public key can check it hasn’t been altered.
• OIDC (OpenID Connect) = a login recipe for humans built on OAuth2. It tells apps how to log people in (redirects, consent) and returns an ID Token (a JWT) that says who the user is.
• Access Token (often a JWT) = a permit you show to an API to prove what you’re allowed to do.
• Refresh Token = a backstage pass the app uses to quietly get new access tokens without asking the user to log in again.

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1) What is JWT?

A compact, URL-safe token format: header.payload.signature.

• Header: the signing algorithm (e.g., RS256).
• Payload: claims like sub (subject/user), aud (audience), exp (expiry).
• Signature: proves the token was issued by the trusted issuer and not modified.

Key property: self-contained. You can validate it offline using the issuer’s public key (published via JWKS URL).

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2) What is OIDC?

A standard way to log users in (web/mobile) using OAuth2. It defines:

• ID Token (JWT) → proves who the user is (identity).
• UserInfo endpoint → optional place to fetch profile data.
• Discovery document → where the app finds all endpoints & keys.

OIDC ≈ login flows; JWT ≈ the token format OIDC uses for identity.

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3) Why do we need them?

• Single Sign-On across apps, teams and even companies.
• Zero shared secrets between every service—verify tokens with public keys.
• Stateless performance—no per-request DB lookup needed to validate tokens.
• Portable and interoperable—works across clouds and languages.

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4) Common use-cases

Human users (OIDC)

• “Login with Google/Okta/Azure AD/Keycloak/Cognito.”
• Multi-app SSO (one login, many apps).
• MFA, passwordless, social login.

Service ↔ Service (JWT)

• One microservice calling another with a short-lived JWT (often from OAuth2 Client Credentials).
• Jobs, webhooks, backends calling APIs without a human user.

Mixed

• User logs in (OIDC) → frontend calls your API with an access token (JWT).
• Backend calls downstream services using its own service JWT.

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5) How they work (step by step)

A) OIDC “Authorization Code + PKCE” (recommended for web/SPAs/mobile)

1. User opens your app → “Sign in”.
2. App redirects the user to the Identity Provider (IdP) (e.g., Google/Okta/Keycloak/Cognito/Firebase).
3. User authenticates (password, MFA, passkey).
4. IdP redirects back with a code.
5. Your app (or backend) exchanges the code at the IdP’s Token Endpoint → gets:
   • ID Token (JWT) = who the user is.
   • Access Token (often JWT) = what they can do.
   • Refresh Token (optional) for silent renewals.
6. App calls your APIs with the access token in Authorization: Bearer <token>.
7. APIs validate the token (issuer, audience, signature, expiry) and proceed.

PKCE: protects SPAs/mobile apps by proving the app that started the login is the app finishing it.

B) Service-to-Service (OAuth2 Client Credentials)

1. Service A asks the IdP/Authorization Server for a token using its client id/secret (or mTLS).
2. IdP issues a short-lived access token (JWT) with claims like aud=ServiceB, scopes/roles.
3. Service A calls Service B with Authorization: Bearer ….
4. Service B validates: signature, issuer, audience, exp (and optionally scope/role claims).

C) Token validation (what every API should check)

• Signature: verify with the issuer’s JWKS public key.
• Issuer (iss): matches the IdP you trust.
• Audience (aud): matches your API.
• Expiry (exp) and not before (nbf).
• Subject (sub) present; optionally scope/roles to authorize actions.

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6) Advanced (without the jargon)

• Scopes vs Roles vs Claims
  • Scopes = what actions are allowed (e.g., read:orders).
  • Roles = grouped permissions (e.g., admin, editor).
  • Claims = facts inside the token (email, org, roles, tenant).
• Key types
  • HS256 (shared secret) → simple but you must protect the secret on every verifier.
  • RS256/ES256 (public/private keys) → issuer keeps private key, everyone else only needs public key (safer & common).
• Key rotation
  • IdP exposes JWKS. Your gateways/servers should cache keys and auto-refresh (handle kid changes seamlessly).
• Refresh tokens
  • Keep them server-side or in HTTP-only secure cookies (not localStorage).
  • Rotate on use; revoke on breach.
• Opaque vs JWT access tokens
  • Opaque: must call the issuer’s introspection endpoint each time.
  • JWT: validate offline; faster, but revocation is trickier.
• Proof-of-Possession (DPoP/mTLS)
  • Binds the token to a specific client key or TLS certificate → blocks token theft/replay.
• Token exchange / impersonation
  • Trade one token for another (e.g., user token → service token limited to one API).
• Logout
  • Front-channel (browser) or back-channel (server-to-server) logout, plus session cookies invalidation and refresh token revocation.

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7) Limitations & gotchas (and how to avoid them)

• Revocation is hard with JWT
  Use short lifetimes (e.g., 5–15 min) + refresh tokens. Revoke refresh tokens on logout/compromise.
• Too many claims = big tokens
  Keep tokens lean; fetch extra data from your user/profile API when needed.
• Audience/issuer mismatches
  Many 401s boil down to wrong aud or iss. Double-check both.
• Clock skew
  Allow 1–2 minutes skew on iat/nbf/exp.
• Storing tokens in the browser
  Prefer HTTP-only secure cookies over localStorage (defense against XSS).
• “alg: none” / weak algorithms
  Only accept expected algorithms (e.g., RS256). Never allow none.

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8) Where they fit in AWS, Google Cloud, Azure

AWS (Amazon)

• Issuers / IdPs
  • Amazon Cognito User Pools (OIDC & OAuth2; issues ID/Access/Refresh tokens as JWTs).
  • IAM OIDC/Federation (workload identity, GitHub Actions, IRSA for EKS).
  • External IdPs: Okta, Auth0, Keycloak, Google (federated to Cognito or directly to ALB/API GW).
• Validators / Enforcement
  • API Gateway (HTTP API) → JWT Authorizer (validates issuer/jwks/audience).
  • Application Load Balancer → authenticate-oidc action (runs the OIDC login flow) with Cognito/Okta/Keycloak/Google (note: not Firebase as an OIDC provider for ALB).
  • EKS: NGINX/Kong/Envoy/Istio gateways can validate JWTs; IRSA uses OIDC to map pods to IAM roles.
  • CloudFront: integrates with Cognito/custom auth at the edge (via Lambda@Edge).

Google Cloud

• Issuers / IdPs
  • Identity Platform / Firebase Auth (OIDC/OAuth2; issues ID tokens as JWTs).
  • Google Workspace/Cloud Identity for enterprise SSO.
• Validators / Enforcement
  • API Gateway / Cloud Endpoints → JWT/OIDC validation in the gateway config.
  • Cloud Run: private services trust Google-signed ID tokens (IAM); put Gateway in front to validate external JWT/OIDC.
  • IAP (Identity-Aware Proxy) for web access control.
  • Load balancers + Cloud Armor (policy/WAF) in front of Gateways/Backends.

Microsoft Azure

• Issuers / IdPs
  • Microsoft Entra ID (formerly Azure AD) and Entra ID B2C (OIDC/OAuth2).
• Validators / Enforcement
  • API Management (APIM) → validate JWT (issuer/jwks/audience), add policies.
  • App Service Authentication (“EasyAuth”) → offload OIDC login to Entra/others.
  • AKS: NGINX/Kong/Envoy/Istio for JWT validation; Workload Identity uses OIDC to map pods to Azure managed identities.

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9) Quick recipes you can reuse

✅ Human login (web/app) — safest baseline

• OIDC Authorization Code + PKCE
• IDP: Cognito / Entra ID / Identity Platform (Firebase Auth) / Okta / Auth0 / Keycloak
• Store access/refresh tokens in HTTP-only secure cookies
• Rotate refresh tokens; short access token TTL (5–15 min)

✅ Service → Service

• OAuth2 Client Credentials (mTLS if possible)
• Short TTL (5–10 min), audience-scoped to the target service
• Validate on the API: signature, iss, aud, exp, scopes/roles

✅ Ingress/Gateway enforcement

• AWS: API Gateway JWT Authorizer or ALB OIDC (with Cognito/Okta/etc.)
• GCP: API Gateway (JWT/OIDC) → Cloud Run (private)
• Azure: APIM JWT policy or EasyAuth

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10) Security checklist (copy/paste)

• Access tokens expire ≤ 15 minutes; refresh tokens rotate.
• Validate signature, iss, aud, exp/nbf on every API call.
• Accept only the algorithms you expect (e.g., RS256).
• Enforce least privilege with scopes/roles.
• Use PKCE for SPAs/mobile.
• Use HTTP-only secure cookies for tokens on the web.
• Implement logout (revoke refresh tokens, clear cookies, end IdP session).
• Monitor JWKS fetch/rotation; handle kid changes.
• Add WAF/rate limits at your gateway/load balancer.
• Log token ID (jti), sub, aud (no sensitive data) for audits.

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11) FAQ (super short)

Is JWT only for machines and OIDC only for humans?

• JWT is a format used by both. OIDC is a login protocol for humans that uses JWT (ID Token).

Do I need OIDC for service-to-service?

• Usually no. Use OAuth2 Client Credentials (returns a JWT access token).

Can I revoke a JWT immediately?

• Not cleanly. Use short lifetimes + refresh token revocation. For high-risk actions, re-check with the IdP or use introspection.

What’s the difference between an ID Token and an Access Token?

• ID Token: identity of the user (for your client).
• Access Token: permission for an API (what can be done).

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12) Your migration hint (EKS front door options)

• Mirror GCP approach: AWS API Gateway (HTTP API) JWT Authorizer validating Firebase/Auth0/Okta/Keycloak → VPC Link → EKS.
• All inside EKS: ALB Ingress → in-cluster gateway (NGINX/Kong/Envoy) validates JWT.
• ALB runs login: use Cognito/Okta/Keycloak/Google for ALB OIDC (Firebase doesn’t act as ALB’s OIDC IdP).

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let’s expand that simple table into detailed workflows so you can see exactly what happens at each hop, for Human login (OIDC), Service-to-Service (JWT), and API Gateway validating JWTs.

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🔄 Detailed Workflows

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1. 👤 Human Login (OIDC → issues JWT ID Token)

Actors: User, Application (frontend + backend), Identity Provider (Google, Okta, Cognito, Firebase, etc.), API

Step-by-step

1. User opens app
   • User clicks “Sign in”.
   • App redirects them to the IdP (OIDC provider).
2. IdP Login Page
   • User enters username/password, MFA, or social login.
   • IdP authenticates them.
3. Authorization Code issued
   • After login, IdP redirects back to app with a code (short-lived, single use).
   • This avoids exposing tokens in browser URL.
4. App exchanges code for tokens
   • App/backend calls IdP Token Endpoint with:
     • The code
     • Client ID/secret
     • PKCE verifier (for extra security in mobile/SPAs)
   • IdP responds with:
     • ID Token (JWT) → “User is Alice”
     • Access Token (JWT/opaque) → “Alice can call API X”
     • Refresh Token (optional).
5. App calls API with Access Token
   • Authorization: Bearer <access_token>.
6. API validates Access Token
   • Check signature (using IdP’s JWKS keys).
   • Check claims (iss, aud, exp).
   • Enforce scopes/roles.
7. API returns response
   • If valid, API serves data → app → user.

✅ Key JWT role here: OIDC issues an ID Token (JWT) for identity, and an Access Token (often JWT) for authorization.

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2. 🔗 Service-to-Service (JWT directly, OAuth2 Client Credentials)

Actors: Service A (caller), Service B (target API), Identity Provider / Authorization Server

Step-by-step

1. Service A needs to call Service B
   • Example: Payment service → Order service.
2. Service A requests token
   • Calls IdP’s Token Endpoint with:
     • client_id, client_secret (or mTLS certificate).
     • Grant type: client_credentials.
3. IdP issues Access Token (JWT)
   • Payload includes:
     • iss (issuer = IdP)
     • aud (audience = Service B)
     • sub (subject = Service A)
     • exp (expiry, e.g., 5 mins)
     • scope (permissions like orders:read).
4. Service A calls Service B
   • HTTP request with Authorization: Bearer <access_token>.
5. Service B validates token
   • Retrieves IdP’s JWKS keys.
   • Verifies signature, expiry, audience = Service B.
   • Enforces scopes (only allowed actions).
6. Service B responds
   • Request succeeds if valid.
   • Otherwise returns 401 Unauthorized.

✅ Key JWT role here: The JWT itself is the service identity. No human involved.

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3. 🌐 API Gateway validates JWT (edge enforcement)

Actors: Client (user or service), API Gateway (AWS API Gateway / GCP API Gateway / Azure APIM / NGINX/Kong), Backend service

Step-by-step

1. Client sends request
   • Attaches Authorization: Bearer <token> (could be user OIDC token or service JWT).
2. Gateway receives request
   • Gateway is configured with issuer and JWKS URI.
3. Gateway validates JWT
   • Check signature against IdP’s public keys.
   • Check issuer matches trusted IdP.
   • Check audience claim matches the API.
   • Check expiry.
   • Optionally check scopes/roles.
4. If valid → forward request to backend.
   • Adds headers (like X-User-Id, X-Scopes) if configured.
   • Backend trusts Gateway because it knows only validated requests get through.
5. If invalid → reject at Gateway.
   • Return 401 Unauthorized (or 403 Forbidden).
   • Backend never sees bad traffic.

✅ Key JWT role here: Gateway uses JWT to decide at the edge whether traffic should even hit the backend.

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📊 Connected View (How they all tie together)

(1) Human Login (OIDC)
User -> OIDC Provider -> ID Token (JWT) + Access Token -> API Gateway -> API

(2) Service-to-Service (JWT)
Service A -> IdP (OAuth2 Client Credentials) -> Access Token (JWT) -> Service B

(3) API Gateway (Validator)
Any Client -> API Gateway -> JWT Validation -> Backend Service

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🔑 Takeaway

• JWT = the envelope (claims + signature).
• OIDC = the login flow (for humans) that issues JWTs.
• Service-to-service uses JWTs directly (no OIDC flow needed).
• Gateways act as bouncers, validating JWTs before APIs are touched.

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