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OpenID Connect Complete Guide: Identity Layer for OAuth2

In this tutorial, you'll learn about OpenID Connect Complete Guide. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

OpenID Connect (OIDC) is an identity layer built on top of OAuth2 that verifies user identity and provides basic profile information through ID tokens and a UserInfo endpoint.

What You'll Learn

How OIDC extends OAuth2 with authentication (ID tokens, claims)
The ID token structure and standard claims
UserInfo endpoint for retrieving identity data
Discovery URL and well-known configuration
OIDC scopes, authentication requests, response types, and flows

Why Openid Connect Matters

OAuth2 alone only handles authorization — it tells you what the client can do, not who the user is. OIDC adds authentication by returning a signed ID token containing the user's identity. Doda Browser uses OIDC for "Sign in with Google" — the ID token provides user identity (name, email, avatar) while OAuth2 handles API access permissions.

flowchart LR
    A["OIDC Guide\n(You are here)"] --> B["ID Tokens\n& Claims"]
    B --> C["UserInfo\nEndpoint"]
    C --> D["Discovery\n& Config"]
    D --> E["Auth Requests\n& Flows"]
    E --> F["OIDC Project"]
    style A fill:#dbeafe,stroke:#2563eb
    style F fill:#dcfce7,stroke:#16a34a

ℹ️ Info

Prerequisites: Solid understanding of OAuth2 concepts (grants, tokens, scopes) from the OAuth2 guide.

Practice Questions

What is the main difference between OAuth2 and OpenID Connect?
What information does an ID token contain?
What is the purpose of the UserInfo endpoint?
How does the discovery URL help OIDC clients?
What is the openid scope used for?

Answers:

OAuth2 handles authorization (what the app can do); OIDC adds authentication (who the user is) through ID tokens.
The ID token contains claims about the user's identity: issuer, subject, audience, expiration, and optionally name, email, picture.
The UserInfo endpoint returns standard claims about the authenticated user (name, email, picture) in JSON format.
The discovery URL (.well-known/openid-configuration) returns the provider's OIDC configuration — authorization endpoint, token endpoint, UserInfo endpoint, supported scopes, JWKS URI.
The openid scope is required for OIDC requests. It signals that the client wants an ID token in addition to the access token.

What's Next

Start with OpenID Connect Introduction to understand how OIDC adds identity to OAuth2.

Start with Lesson 1: OIDC Introduction

Next: API Gateway

Published Topics

OpenID Connect Introduction — Authentication Layer for Modern Applications

Learn what OpenID Connect is, how it adds authentication on top of OAuth2, and why ID tokens and the UserInfo endpoint enable secure user identity verification.

OIDC vs OAuth2 — Key Differences Between Authentication and Authorization

Understand the key differences between OpenID Connect and OAuth2, when to use each protocol, and how they work together for secure user authentication and API access.

Understanding ID Tokens — Structure, Claims, and Verification in OIDC

Learn how OIDC ID tokens work as JWTs, their standard claims (sub, aud, exp, iss), verification process, and how to extract user identity securely.

ID Token Claims — Complete Reference for Standard and Custom OIDC Claims

Learn about all standard OIDC ID token claims including sub, iss, aud, exp, iat, auth_time, nonce, at_hash, and custom claims from the provider.

UserInfo Endpoint — Retrieving User Identity Data in OpenID Connect

Learn how the OIDC UserInfo endpoint returns additional user claims via API, how to call it with an access token, and how it complements the ID token.

Discovery URL — OIDC Provider Configuration and Endpoint Discovery

Learn how the OpenID Connect discovery URL provides provider metadata, endpoints, and supported features via the well-known configuration document.

Well-Known Configuration — Complete OIDC Provider Metadata Reference

Learn every field in the OIDC well-known configuration document, how providers extend it, and how to use it for secure dynamic client configuration.

OIDC Scopes — Controlling Access to User Claims in OpenID Connect

Learn how OIDC scopes like openid, profile, email, address, and phone control which user claims are returned in the ID token and UserInfo response.

OIDC Authentication Request — Building Authorization URLs for User Login

Learn how to build OIDC authentication requests with parameters like client_id, redirect_uri, response_type, scope, state, and nonce for secure user login.

OIDC Response Types — How Tokens Are Delivered in Authentication Responses

Learn about OIDC response types including code, id_token, token id_token, and hybrid flows, and how each delivers authentication results to the client.

OIDC Flows — Authorization Code, Implicit, and Hybrid Authentication Flows

Learn the complete OIDC authentication flows: authorization code flow, implicit flow, and hybrid flow, with step-by-step implementation and security analysis.

OIDC Project — Build a Complete OpenID Connect Authentication System

Build a production-ready OpenID Connect authentication system with user login, token verification, session management, and support for multiple OIDC providers.

ID Token Audience Validation — Verifying the Recipient of a JWT

Learn how audience (aud) claim validation ensures an ID token was issued for your specific application, preventing token interception and replay attacks in OpenID Connect.

OIDC Claims Request — Requesting Specific User Attributes from the Provider

Learn how the claims request parameter in OpenID Connect lets you specify exactly which user attributes to return, reducing payload size and controlling data exposure.

OIDC Claims Distribution — Distributed and Aggregated Claims Explained

Learn how OpenID Connect handles claims from multiple sources using distributed and aggregated claims, enabling identity federation across different providers and services.

OIDC Pairwise Identifiers — Privacy-Preserving Subject Identification

Learn how pairwise identifiers in OpenID Connect provide different sub values for different applications, preventing cross-application user tracking while maintaining consistent identity.

OIDC Dynamic Client Registration — Automating Provider Onboarding

Learn how OpenID Connect Dynamic Client Registration allows applications to automatically register with OIDC providers via API, eliminating manual client setup and configuration.

OIDC Client Types — Web, Mobile, and SPA Application Considerations

Learn how OpenID Connect client types differ for web apps, mobile apps, and single-page applications, including token storage, redirect URIs, and PKCE requirements.

OIDC Security — Protecting Against Replay Attacks, CSRF, and Token Theft

Learn critical OpenID Connect security measures including nonce-based replay prevention, state parameter CSRF protection, token binding, and secure token storage best practices.

Popular OIDC Providers — Keycloak, Auth0, Okta, Azure AD Compared

Learn how major OpenID Connect providers differ in features, pricing, setup complexity, and use cases to choose the right identity platform for your application.

OIDC Testing Strategies — Mock Providers, Token Generators, and Integration Tests

Learn how to test OpenID Connect authentication flows using mock OIDC providers, token generators, and automated integration tests without relying on production identity services.

OIDC Hybrid Flow — Combining ID Token and Access Token in One Request

Learn how the OpenID Connect hybrid flow returns an ID token and access token directly from the authorization endpoint, enabling immediate identity verification before token exchange.

OIDC Session Management — Tracking and Maintaining User Sessions Across Applications

Learn how OpenID Connect manages user sessions at the provider level, enabling single sign-on across multiple applications and session tracking without repeated logins.

OIDC Session Logout — RP-Initiated and OP-Initiated Logout Mechanisms

Learn how OpenID Connect handles logout through RP-initiated logout (application triggers logout) and OP-initiated logout (provider triggers logout across all applications).

OIDC Check Session Iframe — Cross-Application Session State Monitoring

Learn how the OpenID Connect check_session_iframe enables client applications to monitor provider session state changes using postMessage communication in hidden iframes.

OIDC Front-Channel Logout — Browser-Based Cross-Application Session Termination

Learn how OpenID Connect front-channel logout uses iframes loaded in the browser to notify multiple applications when a user logs out, ensuring coordinated session termination.

OIDC Back-Channel Logout — Server-to-Server Session Termination

Learn how OpenID Connect back-channel logout notifies applications directly via HTTP POST from the provider, enabling session termination without browser iframes or user interaction.

OIDC Post-Logout Redirect URI — Controlling the Destination After Session Termination

Learn how the post_logout_redirect_uri parameter in OpenID Connect controls where users are redirected after logout, ensuring a smooth user experience and preventing open redirect vulnerabilities.

OpenID Connect Refresh Tokens — Complete Guide to Long-Lived Access

OpenID Connect refresh tokens obtain new access tokens without user interaction, enabling long-lived sessions while maintaining security with short-lived access tokens.

OpenID Connect Logout — Complete Guide to Session Termination

OpenID Connect logout terminates user sessions at the identity provider and optionally at relying parties, supporting single logout for complete session cleanup.

OpenID Connect Encryption — Complete Guide to JWE

OpenID Connect encryption uses JSON Web Encryption (JWE) to encrypt ID tokens and UserInfo responses, protecting sensitive claims from unauthorized access.

OpenID Connect acr — Complete Guide

OpenID Connect acr extends OAuth 2.0 for authentication, covering acr setup, configuration, and best practices.

OpenID Connect claims-parameter — Complete Guide

OpenID Connect claims-parameter extends OAuth 2.0 for authentication, covering claims-parameter setup, configuration, and best practices.

OpenID Connect display — Complete Guide

OpenID Connect display extends OAuth 2.0 for authentication, covering display setup, configuration, and best practices.

OpenID Connect id-token-hint — Complete Guide

OpenID Connect id-token-hint extends OAuth 2.0 for authentication, covering id-token-hint setup, configuration, and best practices.

OpenID Connect login-hint — Complete Guide

OpenID Connect login-hint extends OAuth 2.0 for authentication, covering login-hint setup, configuration, and best practices.

OpenID Connect prompt — Complete Guide

OpenID Connect prompt extends OAuth 2.0 for authentication, covering prompt setup, configuration, and best practices.

OpenID Connect Request Objects — Complete Guide to Signed Requests

OpenID Connect request objects are JWT-signed authorization requests that provide integrity, authenticity, and non-repudiation for OIDC authentication parameters.

OpenID Connect ui-locales — Complete Guide

OpenID Connect ui-locales extends OAuth 2.0 for authentication, covering ui-locales setup, configuration, and best practices.

OpenID Connect Claims Localization — Complete Guide to Multi-Language

OpenID Connect claims localization returns user claims in multiple languages based on the acr_values or ui_locales parameter for internationalized applications.

OpenID Connect discovery — Complete Guide

OpenID Connect discovery extends authentication with provider metadata and key management.

OpenID Connect dynamic — Complete Guide

OpenID Connect dynamic extends authentication with provider metadata and key management.

OpenID Connect jwks — Complete Guide

OpenID Connect jwks extends authentication with provider metadata and key management.

OpenID Connect rsa — Complete Guide

OpenID Connect rsa extends authentication with provider metadata and key management.

OpenID Connect token introspection — Complete Guide

OpenID Connect token introspection extends authentication with provider metadata and key management.

All 45 topics in OpenID Connect Complete Guide: Identity Layer for OAuth2 are published.

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