Multi Factor Authentication

OAuth 2.1 vs OAuth 2.0 - What's the Difference?

Instasafe

Dec 24, 2024 • 4 min read

OAuth 2.1 vs OAuth 2.0 - What's the Difference?

OAuth has a rich history of continuous improvement. First introduced in 2007, OAuth 1.0 was quickly succeeded by OAuth 2.0 in 2012. Now, OAuth 2.1 is emerging as a consolidated version that captures the best practices learned over eight years of real-world implementation.

The evolution from OAuth 2.0 to OAuth 2.1 represents a significant milestone in securing digital interactions. The primary goal of OAuth 2.1 is not to reinvent the wheel but to simplify and secure the existing OAuth 2.0 framework.

This article will break down the main key differences between OAuth 2.0 and OAuth 2.1, explaining why these changes matter and how they impact developers and users alike.

What is OAuth 2.0?

OAuth 2.0 is an industry-standard authorisation framework that allows applications to secure access to user resources without exposing sensitive credentials. Third-party services can trade tokens with each other to get to a user's secure resources.

Unlike traditional login methods, OAuth 2.0 provides granular access control, letting users grant specific permissions to applications without sharing their entire authentication details.

The protocol defines multiple authorisation flows (grant types) to accommodate different types of applications, including web, mobile and desktop clients. It relies on HTTPS for security and uses short-lived access tokens to minimise potential security risks.

Limitations and Challenges in OAuth 2.0

Security Vulnerabilities

While powerful, OAuth 2.0 faces significant security risks. Token interception and improper implementation can expose sensitive user data, and insufficient validation mechanisms may allow unauthorised access.

Complexity in Implementation

Implementing OAuth 2.0 requires extensive technical expertise. Different grant types and complex authorisation flows can lead to configuration errors and potential system vulnerabilities.

Token Management Issues

Access and refresh tokens present ongoing management challenges. Token lifetimes, revocation and secure storage remain critical concerns for developers and security professionals.

Inconsistent Protocol Interpretations

Variations in OAuth 2.0 implementation across platforms create interoperability challenges. Each service may interpret the protocol slightly differently, complicating cross-platform authentication.

User Experience Limitations

Repeated authentication requests and complex consent screens can frustrate users, potentially leading to reduced engagement and trust in authentication systems.

Comprehensive Comparison of OAuth 2.1 vs 2.0

Feature	OAuth 2.0	OAuth 2.1
PKCE (Proof Key for Code Exchange)	Optional, primarily for public clients	Mandatory for all clients Significantly reduces authorisation code interception risks

Implicit Grant	Supported	Completely removed Eliminates security vulnerabilities in single-page applications

Redirect URI Matching	Flexible, allowed wildcards	Exact string matching only Prevents potential open redirect attacks

Refresh Token Handling	Minimal specific guidelines	Must be either one-time use or sender-constrained Enhances token security and reduces misuse potential

Bearer Token Transmission	Allowed in query strings	Prohibited in query strings Prevents token exposure through URLs

Resource Owner Password Credentials Grant	Supported	Removed Encourages more secure delegation patterns

Default Security Approach	Security is largely left to implementation	Built-in security best practices Reduces potential security misconfigurations

Key Security Transformations in OAuth 2.1

PKCE: From Optional to Mandatory

In OAuth 2.0, Proof Key for Code Exchange (PKCE) was optional and primarily recommended for public clients like mobile applications. OAuth 2.1 makes PKCE mandatory for all clients, including confidential ones.

Why does this matter? PKCE protects against authorisation code interception attacks. By requiring a unique code challenge with every authorisation request, OAuth 2.1 significantly reduces the risk of malicious actors intercepting and misusing authorisation codes.

Implicit Grant

One of the most significant changes in OAuth 2.1 is the complete removal of the Implicit Grant. In OAuth 2.0, this grant was commonly used by single-page applications (SPAs) to obtain tokens directly from the authorisation endpoint.

However, the Implicit Grant was inherently insecure. Access tokens were exposed to any JavaScript running in the browser, creating potential vulnerabilities. An attacker could potentially steal tokens stored in localStorage or non-HttpOnly cookies.

OAuth 2.1 recommends that SPAs use the Authorisation Code flow with PKCE instead, dramatically improving security.

Strict Redirect URI Matching

OAuth 2.0 allowed flexible, wildcard-based redirect URI matching, which could introduce security risks. OAuth 2.1 mandates exact string matching for redirect URIs.

This change prevents potential open redirect attacks where an attacker might manipulate the redirect mechanism to send users to malicious websites. By requiring precise URI matches, OAuth 2.1 closes a significant security loophole.

Refresh Token Best Practices

Refresh tokens in OAuth 2.1 must follow stricter security guidelines. The specification recommends two primary approaches:

One-Time Use Refresh Tokens: When a refresh token is used to get a new token, it becomes invalid. Along with the new access token, the authorisation service gives out a new update token.
Sender-Constrained Refresh Tokens: The refresh token is cryptographically bound to the client that originally received it. Technologies like OAuth Token Binding, Mutual TLS and DPoP can achieve this.

These methods significantly reduce the risk of refresh token theft and misuse.

Bearer Token Handling

OAuth 2.1 prohibits sending bearer tokens in URL query strings. This is crucial because query strings are never truly private - they can be logged, cached, or exposed through browser history.

Instead, sensitive tokens should be transmitted via secure methods like HTTPS headers or POST body, ensuring they remain confidential during transmission.

Removed Authentication Flows

Originally included to ease migration to OAuth-compliant systems, this grant allowed applications to directly handle user credentials. OAuth 2.1 removes this grant, pushing developers towards more secure delegation patterns.

Applications using this grant in OAuth 2.0 will need to migrate to the Authorisation Code grant with PKCE for enhanced security.

Practical Implications for Developers

For developers, OAuth 2.1 isn't about learning an entirely new system but about adopting more robust security practices:

Implement PKCE for all authorisation code grants
Use exact redirect URI matching
Avoid storing tokens in client-side storage
Implement secure token rotation mechanisms
Prefer server-side token management

When Can You Use OAuth 2.1?

As of now, OAuth 2.1 is still in draft form, with the latest draft released in May 2024. The specification is being refined through discussions in the Internet Engineering Task Force (IETF) OAuth working group.

However, developers can start preparing by:

Avoiding Implicit and Resource Owner Password Credentials grants
Implementing PKCE
Following recommended token security practices

Conclusion

OAuth 2.1 represents a maturation of the OAuth framework, not a revolution. By consolidating best practices, removing insecure patterns and focusing on robust security, it provides a more secure foundation for authorisation in modern web and mobile applications.

For developers, the message is clear: security is not an afterthought; it's an important part of the planning process. This idea is built into OAuth 2.1, which makes the way forward safer.

By adding extra protection beyond traditional passwords, Instasafe helps organisations safeguard sensitive data and prevent unauthorised access across various platforms and applications. W provide robust Multi-Factor Authentication solutions that fortify your digital security.