Understanding OAuth 2.0 and OpenID Connect | A Simple Guide for Secure Authentication and Authorization

Key takeaways

• OAuth 2.0 grants access to resources and OpenID Connect adds a signed ID token to prove who logged in.
• Use the authorisation code flow with PKCE for apps that run in browsers or phones.
• Never place access tokens in a URL where logs and browser history can store them.

Table of Contents

• What is OAuth 2.0?
• What is OpenID Connect (OIDC)?
• OAuth 2.0 vs. OpenID Connect: What’s the Difference?
• Benefits of OAuth 2.0 and OpenID Connect
• Use Cases for OAuth 2.0 and OpenID Connect
• Conclusion

As more users access more applications, services and devices, securing them needs a reliable, secure and efficient way to handle authentication and authorization. Two of the most widely used protocols to achieve this are OAuth 2.0 and OpenID Connect (OIDC).

If you're a developer, business owner, or even a tech enthusiast, you need to understand these protocols to build secure, scalable and user-friendly applications. Here we explain OAuth 2.0 and OpenID Connect (OIDC) in simple terms.

What is OAuth 2.0?

OAuth 2.0 is an authorization framework that allows third-party applications to access a user's resources without exposing their credentials (like usernames and passwords). Essentially, OAuth 2.0 enables users to grant permission to third-party services to access their data on other websites or apps securely, without needing to share sensitive information.

How OAuth 2.0 Works

OAuth 2.0 operates based on the concept of tokens, which are strings of data used to authenticate and authorize a user. The process typically involves four main parties:

1. Resource Owner: The user who owns the data (e.g., your social media account or Google Drive files).

2. Client: The third-party application that wants to access the resource owner’s data (e.g., a fitness app connecting to your Google Fit account).

3. Authorization Server: The server responsible for verifying the identity of the resource owner and issuing access tokens to the client.

4. Resource Server: The server that holds the protected data (e.g., Google’s API server storing your files or social media posts).

OAuth 2.0 Flow

Here’s a simplified flow of how OAuth 2.0 works:

1. Request Authorization: The client requests authorization from the resource owner by redirecting them to the authorization server (such as Facebook or Google).

2. Grant Permission: The resource owner logs in and grants permission for the client to access specific resources.

3. Obtain Authorization Code: If permission is granted, the authorization server sends an authorization code back to the client.

4. Exchange Code for Access Token: The client exchanges the authorization code for an access token from the authorization server.

5. Access Protected Resources: With the access token, the client can now make API requests to the resource server, retrieving the resource owner’s data.

Why OAuth 2.0 is Important

OAuth 2.0 is widely used because it simplifies the process of securing user data and reduces the risks associated with sharing passwords. Rather than giving full access to sensitive information like usernames or passwords, OAuth 2.0 uses tokens that are more secure, and they can be revoked if needed.

What is OpenID Connect (OIDC)?

OpenID Connect (OIDC) is an authentication protocol built on top of OAuth 2.0. While OAuth 2.0 is primarily concerned with authorization (granting access to resources), OpenID Connect adds an authentication layer to the process. Essentially, OpenID Connect allows clients to verify the identity of the user based on the authentication performed by an identity provider (e.g., Google, Facebook, etc.).

How OpenID Connect Works

While OAuth 2.0 allows the client to access resources, OpenID Connect enables the client to verify the user's identity. OpenID Connect uses OAuth 2.0 to exchange tokens and build an identity framework on top of it.

The key addition in OpenID Connect is the ID Token, which contains information about the user and is issued alongside the OAuth 2.0 access token. The ID Token is a JWT (JSON Web Token), which is a compact and secure way to transfer identity information.

Here’s how OpenID Connect works:

1. User Logs In: The user logs into the authorization server (e.g., Google, Facebook, etc.).

2. Authorization Request: The client sends an authorization request to the authorization server.

3. Authorization Code: The authorization server sends an authorization code to the client, just like in OAuth 2.0.

4. Exchange Code for Tokens: The client exchanges the authorization code for an access token and an ID token.

5. Verify User Identity: The client uses the ID token to verify the user’s identity and retrieves basic profile information such as name, email, and more.

Key Features of OpenID Connect

• Single Sign-On (SSO): OpenID Connect allows users to log in once and access multiple applications without needing to re-enter credentials. This simplifies user experience and enhances security.

• User Profile: The ID token provides basic user profile information, allowing clients to personalize user experiences without requiring users to create separate accounts for each service.

• Secure Authentication: OpenID Connect uses OAuth 2.0’s security mechanisms while adding an authentication layer to verify the identity of the user.

OAuth 2.0 vs. OpenID Connect: What’s the Difference?

Although both OAuth 2.0 and OpenID Connect are related and work together, they serve different purposes:

Benefits of OAuth 2.0 and OpenID Connect

1. Enhanced Security

Both OAuth 2.0 and OpenID Connect help secure applications by ensuring users don’t need to share sensitive login credentials with third-party applications. Instead, they authenticate via trusted identity providers (e.g., Google or Facebook), reducing the risk of password theft and phishing attacks.

2. Improved User Experience

With OpenID Connect, users can log in once and access multiple applications without re-entering credentials (SSO). This streamlines the login process and improves user experience.

3. Smooth Integration

OAuth 2.0 and OpenID Connect are widely adopted standards, making them easy to integrate into modern web and mobile applications. Many third-party identity providers (Google, Facebook, etc.) support these protocols, allowing developers to focus on building features rather than handling complex authentication and authorization mechanisms.

4. Granular Access Control

OAuth 2.0 allows applications to request only the specific permissions they need, making it easier to implement the principle of least privilege. For example, an app may only ask for read access to your calendar, not your email or contacts.

5. Scalability

OAuth 2.0 and OpenID Connect are highly scalable, allowing businesses to manage authentication and authorization across large user bases, multiple devices and applications.

Use Cases for OAuth 2.0 and OpenID Connect

1. Third-Party Login (SSO)

OAuth 2.0 and OpenID Connect are commonly used to implement single sign-on (SSO) solutions, where users can log in to a third-party website or service using credentials from their trusted identity provider (like Google or Facebook).

2. Mobile and Web Apps

OAuth 2.0 and OpenID Connect are heavily used in mobile and web apps to allow users to access resources across different services without requiring multiple logins.

3. API Access

OAuth 2.0 is frequently used to provide secure API access to third-party services. For example, a weather app may use OAuth 2.0 to access a weather service's API without needing the user’s credentials.

Conclusion

OAuth 2.0 and OpenID Connect are two protocols for securing modern applications. While OAuth 2.0 handles authorization, granting third-party apps access to your data securely, OpenID Connect adds a layer of authentication, verifying your identity to ensure you are who you claim to be.

By adopting these protocols, businesses and developers can offer users a smooth and secure experience while reducing the complexity of managing credentials and ensuring the security of user data. Whether you're building a web or mobile app, understanding OAuth 2.0 and OpenID Connect will help you create a more secure and user-friendly application.

To take this further with guided labs and an instructor, see our web application security training.

Related reading

• What are the most commonly used authentication mechanisms in cybersecurity and how do they work?
• What are the modern authentication methods used in cybersecurity in 2026?
• What Happens Behind the Scenes of a Single Sign-On (SSO) Login?

Reference

For the authoritative details, see IETF RFCs.