OAuth 2.0 Complete Guide: Authorization Framework for Modern APIs

In this tutorial, you'll learn about OAuth 2.0 Complete Guide. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

OAuth 2.0 is an authorization framework that enables third-party applications to obtain limited access to user resources without exposing credentials, defined by RFC 6749.

What You'll Learn

The four OAuth2 roles: Resource Owner, Client, Authorization Server, Resource Server
All grant types: Authorization Code, Implicit (deprecated), Client Credentials, ROPC, PKCE
Access tokens, refresh tokens, scopes, and redirect URIs
Building authorization servers and resource servers
Security vulnerabilities and attack mitigation strategies

Why OAuth2 Matters

Sharing passwords with third-party apps is dangerous. If an app is compromised, the attacker gets your password. OAuth2 solves this by issuing scoped, revocable tokens. DodaTech's Doda Browser uses OAuth2 for "Sign in with Google" and "Sign in with GitHub" — users grant specific permissions (profile, email) without exposing their credentials.

flowchart LR
    A["OAuth2 Guide\n(You are here)"] --> B["Roles &\nGrant Types"]
    B --> C["Authorization\nCode & PKCE"]
    B --> D["Client Credentials\n& ROPC"]
    C --> E["Tokens &\nScopes"]
    D --> E
    E --> F["Security &\nAttacks"]
    F --> G["OAuth2 Project"]
    style A fill:#dbeafe,stroke:#2563eb
    style G fill:#dcfce7,stroke:#16a34a

ℹ️ Info

Prerequisites: Understanding of HTTP, REST APIs, and basic authentication concepts. JWT knowledge helps but is not required.

OAuth2 Grant Types Overview

Grant Type	Use Case	Security
Authorization Code	Web apps with server backend	High (with PKCE)
Implicit (deprecated)	SPAs (legacy)	Low — deprecated
Client Credentials	Machine-to-machine	High
ROPC	Trusted first-party apps	Low — avoid
PKCE	Mobile apps, SPAs	High

Practice Questions

What are the four roles in OAuth2?
Why was the Implicit grant deprecated?
What problem does PKCE solve?
What is the difference between an access token and a refresh token?
How do scopes limit access in OAuth2?

Answers:

Resource Owner (user), Client (app), Authorization Server (issues tokens), Resource Server (holds data).
The Implicit grant exposed access tokens in the URL fragment, making them vulnerable to interception. PKCE provides a more secure alternative for public clients.
PKCE prevents authorization code interception attacks where an attacker intercepts the authorization code on a public client (mobile app or SPA).
Access tokens authorize specific requests and have short expiry; refresh tokens are long-lived credentials that obtain new access tokens without user interaction.
Scopes define the specific permissions the client requests (e.g., read:profile, write:posts). The user consents to each scope, limiting what the client can do.

What's Next

Start with OAuth2 Introduction to understand the core concepts, then explore each grant type in detail.

Start with Lesson 1: OAuth2 Introduction

Next: OpenID Connect

Published Topics

OAuth 2.0 Introduction — Authorization Framework for Delegated Access

Learn OAuth 2.0 fundamentals: how delegated authorization works, the four roles, grant types, tokens, and why OAuth2 is the standard for third-party access.