Authlib: OAuth 2.0 & OpenID Connect Authentication in Python

Introduction

Modern web applications and APIs demand a robust and flexible authentication system. OAuth 2.0 and OpenID Connect have become the de facto standards for this task. However, implementing them correctly requires careful attention to numerous security details. The Authlib library was created to simplify this process in Python.

Authlib is a comprehensive authentication library for OAuth and OpenID Connect that lets you quickly and securely integrate third-party login services, as well as build your own OAuth server. In this guide, we'll walk through how to use Authlib in practice, explore its key features, and show you how to avoid common pitfalls.

OAuth and OpenID Connect Basics

How the Protocols Work

OAuth 2.0 is an authorization protocol that allows an application to access a user's resources without sharing their username and password. Instead, it uses temporary access tokens that can be limited in scope and duration.

OpenID Connect (OIDC) is an extension of OAuth 2.0 that adds an authentication layer. It not only grants access to resources but also verifies the user's identity and provides profile information.

Key Differences Between OAuth and OpenID Connect

OAuth 2.0 lets you access third-party APIs (e.g., listing files in Google Drive, posting to social media) but does not provide user identity information.

OpenID Connect delivers structured user data (email, name, profile picture, etc.) through ID tokens and a userinfo endpoint.

Core Roles in OAuth 2.0

• Resource Owner — the owner of the resource (typically the user)
• Client — the application requesting access to the resource
• Authorization Server — the server that authenticates the user and issues tokens
• Resource Server — the server hosting the protected resources

Overview of the Authlib Library

Project History and Goals

Authlib was created by Lepture (Hsiaoming Yang), who is also the author of several other popular Python libraries. The project launched in 2017 with the goal of providing a complete solution for OAuth and OpenID Connect within the Python ecosystem.

Unlike many other libraries, Authlib offers a unified API for both client and server implementations, along with support for the latest security standards. The library is actively maintained and supported by the community.

Key Features of Authlib

• Full Standard Support: OAuth 1.0a, OAuth 2.0, OpenID Connect 1.0
• Cryptographic Capabilities: JWT, JWS, JWK, JWE
• Ready-Made Integrations: Flask, Django, Starlette, FastAPI
• Security by Default: PKCE, state validation, nonce verification
• Flexibility: Build both client-side and server-side solutions

Library Architecture

Authlib is built with a modular architecture:

• Core — base classes and functions for protocol handling
• Integrations — web framework integrations
• JOSE — JSON Web Tokens and cryptography
• OAuth1/OAuth2 — OAuth protocol implementations
• OIDC — OpenID Connect extensions

Installing and Configuring Authlib

Installation via pip

pip install Authlib

Additional Dependencies

Depending on your web framework, you may need to install extra packages:

# For Flask
pip install Authlib[flask]

# For FastAPI/Starlette
pip install Authlib[starlette]