PKCE

Proof Key for Code Exchange (PKCE) has become a standard security enhancement to the OAuth 2.0 Authorization Code Flow—especially in public clients like mobile and single-page applications. But PKCE isn’t just for frontend apps. When combined with a stateless backend built with Kotlin and Spring Boot, it strengthens your security posture, particularly when you’re avoiding client secrets. This guide walks you through how to implement a secure PKCE flow using Kotlin and Spring Boot, including endpoint structure, code challenge generation, and token exchange. ...

Proof Key for Code Exchange (PKCE) has become a critical enhancement to the OAuth 2.0 Authorization Code Flow, especially for public clients such as mobile and single-page applications. By adding a cryptographically secure verification step, PKCE significantly reduces risks like authorization code interception and replay attacks. What is PKCE and Why Was It Introduced? Originally designed for native and public clients unable to securely store a client secret, PKCE addresses a fundamental security gap in OAuth 2.0. It prevents attackers from stealing authorization codes and exchanging them for access tokens because the authorization code is bound to a one-time generated secret known only to the client. ...

Single Page Applications (SPAs) face unique challenges when implementing OAuth 2.0 authorization flows due to their inability to securely store client secrets. The Authorization Code Flow with PKCE provides a secure, modern approach to handle user authentication and authorization in SPAs while protecting against common attacks such as code interception. Why Use Authorization Code Flow with PKCE for SPAs? Unlike the traditional Implicit Flow, which exposes access tokens directly in the browser URL and has been deprecated by many providers, Authorization Code Flow with PKCE shifts token exchanges to a secure backend or a secure client-side mechanism. PKCE ensures that authorization codes cannot be intercepted or reused by attackers. ...

OAuth 2.0 offers multiple authorization flows to suit different application types and security requirements. Two of the most discussed flows are the Authorization Code Flow and the Implicit Flow. Understanding their differences, strengths, and weaknesses is essential for developers and architects designing secure and efficient authentication systems. Overview of Authorization Code Flow and Implicit Flow The Authorization Code Flow is designed primarily for server-side applications where the client secret can be securely stored. It involves an intermediate authorization code, which the client exchanges for an access token via a backend server. This adds a layer of security by preventing tokens from being exposed in the browser or user-agent. ...

OAuth 2.0 and OpenID Connect are foundational protocols for modern authentication and authorization. This cluster covers key topics including authorization code flow, PKCE security enhancements, JWT usage, and implicit flow, helping you fully understand use cases and practical implementation details. Related Articles Client Credentials Flow in OAuth 2.0: Complete Guide with Real-World Examples Authorization Code Flow vs Implicit Flow: Which One Should You Use? Understanding the Authorization Code Flow in OAuth 2.0 How PKCE Enhances Security in Authorization Code Flow Implementing JWT Bearer Token Grant with ForgeRock: A Practical Guide Understanding Client Credentials Flow in OAuth 2.0: Use Cases and Implementation OAuth 2.0 vs OIDC: Understanding the Key Differences and When to Use Each Implementing Fine-Grained Access Control with JWT JWT Decoding and Validation: Essential Practices for Secure OAuth 2.0 Implementations Stay tuned for the latest deep dives and practical guides on OAuth 2.0 and OpenID Connect. ...

OAuth 2.0 is a widely used authorization framework that allows applications to obtain limited access to user resources without handling user credentials directly. The Authorization Code Flow with PKCE (Proof Key for Code Exchange) is a security-enhanced version of the Authorization Code Flow, specifically designed to address vulnerabilities in public clients like mobile apps and single-page applications (SPAs) that cannot safely store a client secret. Why PKCE Is Needed Traditional Authorization Code Flow relies on a client_secret to authenticate the client when exchanging an authorization code for a token. In public clients (like browser apps or mobile apps), this secret cannot be safely stored. Without proper safeguards, attackers could intercept the authorization code during redirection and exchange it for tokens. ...