Welcome to the world of OpenID – your key to simpler, safer online authentication! In this informative blog, we’ll explore OpenID, break down a few of its types, and provide beginners with authentication and authorization insights.

OpenID is a versatile protocol compatible with various programming languages, including Java, PHP, Perl, C/C++, C##, and Python. Regardless of your tech stack preference, OpenID has got you covered. Let’s dive into the different “flows” within OpenID, each offering unique advantages.

The Big Players: Authorization Code vs. Implicit Flow

Authorization Code Flow

Considered the gold standard in security, this flow involves several steps but provides robust protection.

First, the user requests access to a service or resource at the SP (Service Provider) site.

The SP then redirects the user to the authorization server, where the user is prompted to authenticate themselves. Once the user is authenticated, the authorization server generates an authorization code and redirects the user back to the SP site.

The SP site then exchanges this authorization code for an access token and refresh token by making a direct request to the authorization server. The pros of using the authorization code flow in OpenID are its high level of security and the ability to securely exchange the authorization code for access tokens and refresh tokens.

The cons of the authorization code flow include the additional steps and complexity involved in the process, as well as the potential for increased latency due to the multiple network requests.

PKCE (Proof Key for Code Exchange)

PKCE flow is an extension of the authorization code flow in OpenID that adds an extra layer of security against potential attacks in certain scenarios, such as mobile and native applications. This flow type mitigates the risk of malicious attackers' interception and misuse of the authorization code.

Instead of directly exchanging an authorization code for access tokens, the PKCE flow introduces a "code verifier" and a "code challenge" during the authorization request.

The code verifier is a random string generated by the client, while the code challenge is a transformed version of the code verifier. When the client requests authorization, it includes the code challenge in the authorization request. Upon receiving the authorization code, the client includes the original code verifier in the token request. This verification process ensures that the client making the token request is the same client that originally requested the authorization code, adding an extra security layer. Even if the authorization code is intercepted, it cannot be used to obtain access tokens without the matching code verifier.

Implicit Flow

Prioritizing speed, the Implicit Flow is like the express lane for authentication.

Instead of exchanging an authorization code for access tokens, the user directly receives the access token from the authorization server.

The pros of using implicit flow in OpenID include its simplicity and reduction in complexity compared to authorization code flow. This makes it more suitable for scenarios where a lightweight and seamless user experience is preferred, such as single-page applications.

However, there are some cons to using implicit flow. One significant con is the potential vulnerability to token leakage and replay attacks since access tokens are directly issued in the authorization response. To address the vulnerability of token leakage and replay attacks, some propose using "Identity-Based Encryption" as a mechanism to bind tokens to a specific client cryptographically.

Conclusion

In summary, OpenID offers different flow types to handle user authentication and application access. The implicit flow provides a smooth user experience but comes with risks like token leakage and replay attacks. The authorization code flow is more secure since it separates the steps of authorization and token exchange, though it involves a few extra steps. The PKCE flow builds on the authorization code flow by adding protection against code interception.

Ultimately, choosing the right flow depends on the application's security needs and user experience goals.