OAuth 2.1 is the next major evolution of the OAuth 2.0 authorization framework. It consolidates best practices, removes insecure legacy features, and improves security and developer experience for modern applications.

Why OAuth 2.1?

Since OAuth 2.0’s publication in 2012, the security landscape and application requirements have evolved significantly. OAuth 2.1 aims to:

  • Simplify the specification by removing confusing or risky options.
  • Enforce modern security defaults.
  • Address common implementation mistakes.
  • Support native apps and SPAs securely by default.

Key Changes in OAuth 2.1

  1. Removal of Implicit Flow The implicit flow is deprecated due to inherent security risks like token leakage in browser URLs. OAuth 2.1 mandates using the authorization code flow with PKCE instead.

  2. Mandatory PKCE for Authorization Code Flow PKCE (Proof Key for Code Exchange) is now required for all clients, including confidential and public clients, ensuring safer authorization codes.

  3. Refresh Token Handling Improvements OAuth 2.1 encourages short-lived access tokens and safer refresh token usage patterns to mitigate token theft risks.

  4. Stricter Redirect URI Requirements Redirect URIs must be pre-registered and use HTTPS to prevent open redirect attacks.

  5. More Secure Token Storage Recommendations OAuth 2.1 highlights best practices for securely storing tokens, especially in browser-based applications.

What OAuth 2.1 Means for Developers

  • Legacy apps using implicit flow will need to migrate to PKCE-enabled authorization code flow.
  • Developers can expect fewer implementation pitfalls due to the more prescriptive spec.
  • Increased security reduces risk from token theft and replay attacks.
  • Native apps and SPAs gain better security defaults out of the box.

Example: Authorization Code Flow with PKCE

# Generate code verifier and challenge (example with openssl)
CODE_VERIFIER=$(openssl rand -base64 32 | tr -d '=+/')
CODE_CHALLENGE=$(echo -n "$CODE_VERIFIER" | openssl dgst -sha256 -binary | base64 | tr -d '=+/')

# Authorization request URL
https://auth.example.com/authorize?response_type=code&client_id=client123&redirect_uri=https://app.example.com/callback&code_challenge=$CODE_CHALLENGE&code_challenge_method=S256&scope=openid

This ensures the authorization code can only be exchanged by the client that initiated the request.

Transitioning from OAuth 2.0 to 2.1

  • Audit your apps to identify implicit flow usage.
  • Implement PKCE everywhere, including confidential clients.
  • Review redirect URI registrations and enforce HTTPS.
  • Follow updated token storage and refresh token guidelines.

Resources

Summary

OAuth 2.1 represents a significant step forward in securing OAuth implementations. By eliminating risky legacy flows and enforcing best practices like PKCE, it empowers developers to build more secure and reliable authentication and authorization solutions.

👉 Related:

Authorization Code Flow vs Implicit Flow: Which One Should You Use?

Building a Secure PKCE Flow with Kotlin and Spring Boot

💡 Are your applications ready for OAuth 2.1? What challenges do you anticipate in migrating to the new spec?