OAuth2 vs. OIDC: Demystifying the Authentication and Authorization Protocols

OAuth2 vs. OIDC: In today’s digital landscape, securing user access to web applications and APIs is paramount. To meet this need, various authentication and authorization protocols have emerged. Two of the most prominent ones are OAuth 2.0 (OAuth2) and OpenID Connect (OIDC). While they are closely related and often used together, they serve different primary purposes. In this article, we’ll delve into OAuth2 and OIDC, highlighting their differences and similarities, and provide a comparison table for quick reference.

Understanding OAuth2

OAuth2, which stands for “Open Authorization 2.0,” is a framework for securing access to resources across the web. It’s a versatile protocol that enables a secure and standardized way for applications to access user data on their behalf without exposing their credentials. OAuth2 is commonly used in scenarios where one application (the client) needs to access data or perform actions on behalf of another user, but without the user sharing their login credentials.

Key Components of OAuth2

  • Client: The application requesting access to a resource.
  • Resource Owner: The user who owns the resource.
  • Authorization Server: The server responsible for authenticating the user and issuing access tokens.
  • Resource Server: The server hosting the protected resources.
  • Access Token: A credential that represents the authorization granted to the client.

OAuth2 Flow

OAuth2 defines several authorization flows, but the most common ones include the authorization code flow and the implicit flow. In the authorization code flow, the client obtains an authorization code, which it exchanges for an access token and possibly a refresh token. The implicit flow directly returns an access token to the client. OAuth2 doesn’t standardize user authentication – it focuses on obtaining access tokens for clients.


Introducing OpenID Connect (OIDC)

OpenID Connect (OIDC) is often referred to as “OAuth for Authentication.” While OAuth2 focuses on authorization, OIDC extends it to include authentication. It’s built on top of OAuth2, providing a standardized way for applications to verify the identity of a user based on the authentication performed by an authorization server.

Key Components of OIDC

OIDC introduces a few additional components to the OAuth2 model:

  • ID Token: A JSON Web Token (JWT) that contains claims about the user’s identity.
  • UserInfo Endpoint: An endpoint where additional user information can be retrieved.

OIDC builds upon OAuth2, enhancing it with features that allow clients to obtain identity information about users and ensuring that the user’s identity is properly verified during the authorization process.

OAuth2 vs. OIDC: A Comparison

Now that we’ve introduced both OAuth2 and OIDC, let’s compare them side by side with a handy table:

Feature OAuth2 OIDC
Primary Purpose Authorization Authentication and Authorization
Token Type Access Token Access Token, ID Token
User Identity Not standard; up to the implementation Standardized with ID Token
User Authentication Not standardized Standardized through OIDC authentication
User Information Retrieval Optional; additional requests to the API Standardized through UserInfo Endpoint
Usage Securing APIs, accessing resources Identity verification, single sign-on (SSO)

When to Use OAuth2 and OIDC

Understanding the differences between OAuth2 and OIDC is crucial for choosing the right protocol for your application. Here’s a simple guideline:

  • Use OAuth2 when your application needs to access resources or APIs on behalf of a user, but you don’t require standardized user authentication or identity claims.
  • Use OIDC when you need to verify a user’s identity, obtain standardized identity claims, and enable single sign-on (SSO) for your application.


Frequently Asked Questions (FAQs)

1. Can OAuth2 and OIDC be used together?

Yes, OAuth2 and OIDC are often used together in scenarios where both authorization and authentication are needed. OIDC is built on top of OAuth2 and extends it to provide standardized authentication features.

2. Do I have to use OIDC to authenticate users?

No, OIDC is not mandatory for user authentication. OAuth2 can be used to handle authorization and some aspects of user authentication, but OIDC provides a more standardized and comprehensive solution for authentication.

3. What is the role of an identity provider (IdP) in OIDC?

An identity provider, such as Google, Facebook, or a company’s own authentication service, plays a critical role in OIDC. It’s responsible for authenticating users and providing identity information to clients through the OIDC protocol.

4. How are security and privacy maintained in OAuth2 and OIDC?

Both OAuth2 and OIDC include security mechanisms such as access tokens and ID tokens. Additionally, they support encryption and security best practices to protect user data and maintain privacy.

5. Are there any notable security concerns with these protocols?

Security concerns can arise if these protocols are not implemented correctly. It’s crucial to follow best practices, use secure libraries and frameworks, and regularly update your systems to mitigate potential security risks.


In the world of web application development and API access, OAuth2 and OIDC play pivotal roles in securing user interactions. OAuth2 is primarily an authorization protocol, while OIDC extends OAuth2 to include authentication. By understanding their differences and knowing when to use each, you can make informed decisions when building secure, user-friendly applications.

External Resources:

  1. OAuth 2.0
  2. OpenID Connect

Remember, the choice between OAuth2 and OIDC depends on your specific use case and requirements. While they may seem complex at first, these protocols offer a robust foundation for securing your applications and users’ data.

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