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Spring Security 6 & JWT Authentication · Lesson

Common OAuth2 Grant Types

Explore various grant types like Authorization Code, Client Credentials, and their appropriate use cases.

Common OAuth2 Grant Types is a free Spring Security 6 & JWT Authentication lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Spring Security 6 & JWT Authentication learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

What are OAuth2 Grant Types?

Welcome! In OAuth2, a Grant Type (or 'Authorization Grant') is a method an application uses to get an access token from an authorization server.

Think of it as the specific procedure or negotiation protocol for obtaining permission to access protected resources.

Why Different Grant Types?

You might wonder why there isn't just one way to get a token. Different applications have different security needs and capabilities:

  • Web applications with a backend
  • Single-page applications (SPAs) in a browser
  • Mobile applications
  • Command-line tools
  • Server-to-server communication

Each scenario requires a tailored, secure approach.

Authorization Code Grant

The Authorization Code Grant is the most common and recommended grant type for confidential clients, especially traditional web applications with a backend.

It's considered the most secure because the access token is never exposed directly in the user's browser.

Auth Code Flow: User Authorization

Here's how the Authorization Code flow typically starts:

  1. The user clicks 'Login with X' on your app.
  2. Your app redirects the user's browser to the Authorization Server (e.g., Google, GitHub).
  3. The user logs in and grants permission to your app.
  4. The Authorization Server then redirects the user's browser back to your app with a temporary authorization code.

Auth Code Flow: Token Exchange

After receiving the authorization code:

  1. Your app's backend receives the authorization code.
  2. It then securely exchanges this code (along with its own client ID and client secret) directly with the Authorization Server's token endpoint. This is a server-to-server communication.
  3. The Authorization Server validates the code and client credentials, then issues an access token (and often a refresh token).

Client Credentials Grant

The Client Credentials Grant is used for machine-to-machine communication where there is no end-user involved.

The client (your application or service) acts on its own behalf, authenticating itself directly to the Authorization Server to get an access token.

Client Credentials Flow

The flow for Client Credentials is simpler:

  1. Your client application (e.g., a background service) sends its client ID and client secret directly to the Authorization Server's token endpoint.
  2. The Authorization Server verifies these credentials.
  3. If valid, the Authorization Server directly issues an access token to your client.

No user interaction or browser redirects are needed.

Client Credentials in Action

Imagine a backend service that needs to query an external API to fetch data. It doesn't need a user to log in; it just needs access as 'itself'.

It would use the Client Credentials flow to get an access token:

curl -X POST -u "my-client-id:my-client-secret" \ "https://auth.example.com/oauth/token" \ -d "grant_type=client_credentials"

Device Code Grant

The Device Code Grant is designed for input-constrained devices like smart TVs, IoT devices, or command-line tools that cannot easily host a web browser or accept redirects.

It separates the authorization process, allowing the user to authorize the device on a separate, more capable device (like a smartphone or computer).

Device Code Flow

Here's a simplified Device Code flow:

  1. The device requests a device code and a user verification URI from the Authorization Server.
  2. The device displays the URI and a short code to the user.
  3. The user goes to the URI on their phone/PC, logs in, and enters the code to grant access.
  4. Meanwhile, the device repeatedly polls the Authorization Server until authorization is confirmed, then it receives the access token.

Grant Type Challenge

Based on what you've learned, which OAuth2 grant type is most suitable for a backend service that needs to access another API without any user interaction?

Recap: Grant Types in Focus

We've explored key OAuth2 grant types: Authorization Code for secure web applications with user interaction, Client Credentials for server-to-server communication, and Device Code for input-constrained devices.

Each grant type addresses specific security and usability needs, ensuring secure authorization flows for different application scenarios.

Frequently asked questions

Is the “Common OAuth2 Grant Types” lesson free?

Yes — the full text of “Common OAuth2 Grant Types” is free to read here on the web, and the Spring Security 6 & JWT Authentication course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Spring Security 6 & JWT Authentication course, upgrade to CoddyKit PRO.

What will I learn in “Common OAuth2 Grant Types”?

Explore various grant types like Authorization Code, Client Credentials, and their appropriate use cases. You practise Spring Security 6 & JWT Authentication with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Spring Security 6 & JWT Authentication?

No prior experience is required. Spring Security 6 & JWT Authentication on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Common OAuth2 Grant Types” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Spring Security 6 & JWT Authentication lesson?

Yes. Every Spring Security 6 & JWT Authentication lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. OAuth2 Protocol Overview
  2. OpenID Connect Introduction
  3. Common OAuth2 Grant Types
  4. PKCE and Securing Public Clients
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