Welcome to this in-depth exploration of OAuth 2.0 and OpenID Connect, two fundamental protocols in modern identity and access management. In this article, we'll delve into these protocols step by step, building upon each concept to provide a clear understanding of their roles and applications.
Introduction to OAuth 2.0
OAuth 2.0, the second version of the OAuth protocol, plays a pivotal role in securely authorizing third-party applications to access user data without exposing sensitive credentials. Let's begin by understanding its core purpose and benefits.
Delegated Authority
Consider a scenario where a user wishes to share data between two applications, but the data is protected behind their login credentials. Sharing login credentials with both applications isn't a viable solution as it poses various security and operational challenges. OAuth 2.0 steps in to address this issue by allowing users to grant "delegated authority" to an application without revealing their username and password.
When a user initiates integration between two applications, OAuth 2.0 orchestrates a secure flow where the user logs in to one application (App 2) and grants permission for the integration. App 1 never sees the user's password. Instead, it receives an access token, which it can use to retrieve data from App 2. OAuth 2.0 brings several advantages, such as granular access control and easy revocation of access.
The Four Parties in OAuth 2.0
To better understand how OAuth 2.0 operates, let's break down the four main parties involved:
- Resource Owner: This is the user who owns the data.
- Client: The application to which the user delegates authority.
- Authorization Server: Responsible for generating access tokens.
- Resource Server: Where the user's data resides.
These parties can be hosted together or separately, depending on the implementation. Organizations often run a central authorization server for multiple applications.
OAuth 2.0 in Practice
Let's move on to practical implementations of OAuth 2.0. In this example, we'll explore a native application, like an email client, connecting to an Office 365 backend.
Initial Setup
- The client (email application) connects to the backend but doesn't possess a valid access token.
- It must obtain an access token from the authorization server, which is part of Office 365.
- The user must authenticate into Office 365, a step outside OAuth 2.0.
Access Token and Refresh Token
- Upon successful authentication, the authorization server generates two tokens: an access token and a refresh token.
- Both tokens are sent to the client, which attaches the access token to its requests to the resource server (email data, contacts, etc.).
- The client can perform tasks on behalf of the user without needing the user's credentials.
Token Lifetimes
Access tokens typically have a limited time to live, often around one hour. Refresh tokens have a longer validity, with an idle timeout of, say, 14 days, but it can extend up to 90 days with regular use. This design allows for enhanced security and ease of use.
Server-to-Server Communication
OAuth 2.0 isn't limited to user-initiated flows; it's also widely used for server-to-server communication. In this context, it serves a similar purpose to delegated authority.
Admin Setup
Before users of App 1 can integrate with App 2, the administrators of both applications must coordinate. The admin of App 1 registers their application in App 2, providing essential details like a callback URL and receives a client ID and secret.
User-Initiated Flow
- The user initiates integration by redirecting their browser to App 2 for authentication.
- The user grants consent for specific scopes (access levels) requested by App 1.
- An authorization code is generated and sent to App 1 via the user's browser.
Access Token Exchange
- App 1 sends the authorization code to App 2, along with its client ID and secret, requesting an access token.
- App 2's authorization server generates and sends the access token to App 1.
- This access token authorizes App 1 to access the user's data on App 2.
Why the Authorization Code Grant?
The Authorization Code Grant, a key OAuth 2.0 flow, combines front-channel and back-channel communication for added security. Front-channel communication poses a risk if malicious code intercepts the access token. The exchange of an authorization code for an access token is a secure back-channel operation, ensuring token confidentiality.
Expanding OAuth 2.0 with OpenID Connect
OAuth 2.0, while versatile, was not originally designed for user authentication. This led to misuse in some scenarios. OpenID Connect (OIDC) was introduced as an extension to OAuth 2.0, bringing standardized user authentication.
Key Elements of OpenID Connect
- ID Token: A JWT containing user information.
- User Info Endpoint: Allows the client to retrieve additional user data.
- OpenID Connect Discovery: A standard method for configuration, making integrations more straightforward.
OpenID Connect Flow
In an OpenID Connect scenario, we have two applications: one acts as the client, and the other serves as the OpenID Connect provider.
User Authentication
- The user initiates access to the client (App 1).
- App 1 redirects the user to the OpenID Connect provider (App 2) for authentication.
- The user authenticates into App 2.
ID Token and User Info
- An authorization code is sent back to App 1.
- App 1 exchanges the code for an access token and an ID token.
- The ID token contains user claims.
- If more user data is needed, App 1 can use the access token to access the User Info Endpoint.
Conclusion
In this comprehensive overview, we've explored OAuth 2.0 and OpenID Connect, two essential protocols in modern identity and access management. OAuth 2.0 empowers users to delegate authority securely, while OpenID Connect enhances it with standardized user authentication. These protocols, with their flexibility and security measures, are key components of today's digital ecosystem.
