[Book Review] "Introduction to OpenID Connect" A Book for Making Correct Judgments About Authentication and Authorization Specifications in AI-Driven Development

Hello, I'm Tsukuboshi (tsukuboshi0755)!

I recently read "Introduction to OpenID Connect," and I felt it was a book that allows you to systematically learn the OpenID Connect (hereafter OIDC) specifications, so I'd like to introduce it!

In recent years, code generation using generative AI has rapidly spread, and opportunities to leave authentication and authorization implementation to coding agents have increased. Code for OIDC integration output by AI often "works" in development environments, and at first glance it may appear to have been implemented without issues.

However, authentication and authorization code differs greatly from other code, and specification-level errors directly lead to security incidents. For example, judgments such as whether PKCE is correctly implemented, whether the state parameter is being validated, and whether redirect URI registration is appropriate can only be made by developers who understand the OIDC specification. In this article, I'd like to introduce the recommended points of this book, which provides a basis for judgment on authentication and authorization in the age of AI-driven development!

Book Information

• Release date: 2026/2/24
• Author: Kohei Toki
• Supervisor: Masa Kurabayashi
• Publisher: Gijutsu-Hyoron-sha

https://gihyo.jp/book/2026/978-4-297-15456-1

Note that this book is structured to carefully explain the basics of OAuth 2.0 before moving on to the explanation of OIDC. Therefore, even those with limited knowledge of OAuth 2.0 can read through it without any prerequisite knowledge.

Target Readers

I would recommend this book to those who are implementing authentication features for OIDC or OAuth 2.0 using coding agents such as Claude Code, but feel uneasy because they cannot judge whether the generated code is correct from a specification standpoint.

It is also suitable for those who use managed authentication services such as Amazon Cognito or Okta, but want to understand the mechanism of the protocols working behind the scenes. This book compactly covers everything from OIDC specifications to implementation examples and security measures, and is a condensed collection of knowledge necessary to evaluate authentication implementations.

In particular, I strongly recommend reading this book for those who feel uneasy about whether it is safe to use authentication and authorization implementations written by AI, entrust user credentials to them, and run them in production.

Recommended Points of This Book

The pathway from OAuth 2.0 basics to OIDC is easy to understand

When you leave authentication and authorization implementation to a coding agent, it will output plausible-looking code. However, protocol-level judgments such as which to use between the authorization code flow and the implicit flow, and why PKCE is necessary, cannot be made correctly without understanding the specifications.

This book covers this theme across Chapters 1 to 7, with a structure that allows you to learn step by step, starting from the role of OAuth 2.0 and progressing to how OIDC extends it. The main discussion points are as follows.

• The relationship between OAuth 2.0 and OIDC, and the role of each protocol
• Types of flows such as authorization code flow, implicit flow, and hybrid flow, and how to use them
• Types and formats of access tokens, ID tokens, and refresh tokens
• The mechanism of PKCE (Proof Key for Code Exchange)
• Logout methods (RP Initiated Logout, Front-Channel, Back-Channel)

You will acquire foundational knowledge that is directly useful when evaluating AI-generated authentication and authorization code with questions like "Why is this flow being selected?"

Implementation examples by client type allow you to learn how to differentiate flow usage

In actual development, the correct OIDC flow differs depending on the client type. Whether it's a SPA, whether a BFF is involved, or whether it's a native app, the methods of token management and security considerations vary greatly. Understanding these differences is essential to judge whether the authentication and authorization implementation generated by a coding agent uses a flow appropriate for your application's configuration.

This book covers Chapters 8 to 12 with sample programs using Keycloak, showing implementation examples for each client type.

• Building a practical hands-on environment using Keycloak (Chapter 8)
• Implementation of authorization code flow and PKCE in SPAs (Chapter 9)
• Token management on the server side using BFF (Chapter 10)
• Custom URL schemes and security considerations in native apps (Android apps) (Chapter 11)
• Client credentials flow for machine-to-machine communication (Chapter 12)

In particular, authentication and authorization implementations generated by coding agents tend to have a simple configuration where tokens are handled by the SPA alone, but considering the risk of token theft through XSS, there are many situations in practice where server-side token management using BFF is required. Chapter 10 carefully explains this BFF pattern with Keycloak integration, allowing you to understand the safe architecture that goes one step beyond the code proposed by AI.

Security threats and countermeasures provide a basis for judging AI-generated code

It is not easy to look at OIDC implementation code generated by a coding agent and readily judge whether countermeasures against threats such as CSRF vulnerabilities, token injection, and redirect URI manipulation are sufficient.

Chapter 13 of this book comprehensively covers representative security threats in OIDC and how to address them, and can be used as a checklist when reviewing AI-generated code. The following threats and countermeasures are mainly covered.

• Countermeasures against open redirectors
• Countermeasures against authorization code leakage via Referer headers
• Authorization code injection and defense using PKCE
• CSRF of redirection endpoints and defense using the state parameter
• Countermeasures against Mix-Up attacks (IdP confusion)
• A list of security measures that application developers should implement

Security threats related to authentication, unlike bugs in other code, directly lead to leakage of users' personal information and credentials. The knowledge in this chapter provides specific perspectives for judging whether AI-written code is "safe from a specification standpoint."

Furthermore, this book explains practical real-world recommended values that cannot be understood just by reading specifications, such as "It's good to start with 30 minutes as the basic access token validity period and then adjust from there," drawn from the author's expertise. It is not merely a specification reference book, but is packed with insights that can be directly applied to actual design decisions.

Finally

This time I introduced "Introduction to OpenID Connect."

This book systematically covers everything from the basics of OAuth 2.0 and OIDC specifications to implementation patterns by client type, and security threats and countermeasures, allowing you to develop the judgment needed to confidently evaluate authentication implementations.

This book is especially recommended for engineers who want to be able to judge on their own terms whether AI-generated authentication code is "correct from a specification standpoint and safe from a security perspective." Please do pick it up and give it a read!

That's all from Tsukuboshi (tsukuboshi0755)!