How do you configure OAuth2 resource server in Spring Boot?

Table of Contents

Introduction

In Spring Boot, you can secure your REST API using OAuth2 as a resource server. A resource server is responsible for serving protected resources (e.g., APIs) to authorized clients. It validates access tokens issued by an authorization server (e.g., OAuth2 provider) to ensure that requests are coming from authenticated users.

Spring Security provides built-in support for OAuth2 and JWT (JSON Web Tokens), which are commonly used for securing REST APIs. By configuring your Spring Boot application as an OAuth2 resource server, you can easily secure your endpoints and ensure that only authorized clients can access your resources.

In this guide, we will walk through the process of configuring an OAuth2 Resource Server in a Spring Boot application, focusing on the validation of OAuth2 tokens and securing REST APIs using JWT.

Setting Up OAuth2 Resource Server in Spring Boot

Step 1: Add Dependencies

To enable OAuth2 resource server support in a Spring Boot application, you need to add the necessary dependencies to your project.

For Maven (in pom.xml):

For Gradle (in build.gradle):

These dependencies include the required components to enable OAuth2 resource server support and security in your Spring Boot application.

Step 2: Configure application.properties or application.yml

Next, you need to configure your application to validate OAuth2 access tokens. If you are using JWT (which is common for OAuth2), you will need to provide details about the token issuer and how to validate the tokens.

Example: application.yml

In this configuration:

  • **issuer-uri** points to the base URL of your OAuth2 authorization server. This is used to validate the JWT's issuer.
  • **jwk-set-uri** is used to point to the URL from which the public keys used to sign JWT tokens can be retrieved. This is necessary for validating JWT signatures.

If you're not using JWT tokens, Spring Security also supports other formats for OAuth2 tokens (like opaque tokens), but in most cases, JWT is the preferred format for OAuth2 access tokens.

Step 3: Configure Spring Security for OAuth2 Resource Server

You need to configure Spring Security to enable resource server capabilities and to secure your REST API endpoints. This can be done in a custom SecurityConfig class.

Example: SecurityConfig.java

In this configuration:

  • The .oauth2ResourceServer().jwt() method tells Spring Security to use JWT tokens for OAuth2 resource server functionality.
  • The .jwtAuthenticationConverter() method allows you to customize how roles and authorities are extracted from the JWT claims.
  • The .authorizeRequests() method secures your API endpoints by specifying which ones are public and which require authentication. For example:
    • The /public/** endpoint is open to everyone.
    • The /protected/** endpoint is only accessible by authenticated users.

Step 4: Create REST Endpoints (Protected and Public)

Now, you can create your REST API with public and protected endpoints. The public endpoints are accessible without authentication, while the protected endpoints require OAuth2 authentication.

Example: ApiController.java

In this example:

  • /api/public is accessible by anyone (no authentication required).
  • /api/protected is only accessible to authenticated users, and it retrieves the authenticated user’s information from the JWT token (e.g., the user's name).

Step 5: Test the OAuth2 Resource Server

To test your OAuth2 resource server, you need to perform the following steps:

  1. Obtain a valid OAuth2 access token from your authorization server (e.g., by logging in via an OAuth2 provider like Google, GitHub, or your custom OAuth2 server).

  2. Make an authenticated request to the protected API endpoint (/api/protected), attaching the access token in the Authorization header.

    Example of an HTTP request:

  3. Ensure that your API responds correctly, granting access to protected resources only if the access token is valid.

Conclusion

Configuring an OAuth2 resource server in Spring Boot allows you to secure your REST APIs using OAuth2 tokens, such as JWTs. By enabling OAuth2 resource server support and configuring Spring Security to validate and authenticate access tokens, you ensure that only authorized clients can access sensitive resources.

This setup is particularly useful for microservices architectures, where you might have multiple services that require centralized authentication and authorization. Spring Boot’s built-in support for OAuth2 resource server simplifies the process of securing your APIs, making it easier to integrate with OAuth2 authorization servers and enforce access control policies across your application.

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