How do you configure CORS for Spring Security?

Table of Contents

• Introduction
• What is CORS and Why Is It Important?
• Configuring CORS in Spring Security
  • 1. Basic CORS Configuration in Spring Security
  • 2. Configuring CORS with Spring Security’s HttpSecurity
  • 3. Using a Custom CORS Filter
  • 4. Enabling CORS for Specific Endpoints
• Practical Examples of CORS Configuration
  • Example 1: Allowing All Origins for Public APIs
  • Example 2: Restricting CORS to Specific Domains
• Conclusion

Introduction

CORS (Cross-Origin Resource Sharing) is a security feature that allows web applications running at one origin (domain) to make requests to resources hosted on a different origin. In modern web development, especially when building APIs that interact with frontend applications deployed on different domains, configuring CORS properly is crucial for ensuring security and functionality.

In Spring Security, CORS needs to be configured in order to control how resources can be shared across different origins. By default, browsers block cross-origin requests for security reasons, but with CORS, we can specify which domains are allowed to access specific resources. This tutorial will walk through the steps to configure CORS in Spring Security.

What is CORS and Why Is It Important?

CORS is a protocol that enables web applications to make requests for resources hosted on different domains or subdomains. For example, if a frontend React app is hosted on http://localhost:3000 and your Spring Boot backend is hosted on http://localhost:8080, the frontend needs to make cross-origin requests to fetch data or interact with the backend.

Without proper CORS configuration, the browser will block such requests. This is where configuring CORS in Spring Security becomes essential.

Configuring CORS in Spring Security

Spring Security provides the ability to configure CORS in your application through several methods. Here are the common ways to enable and customize CORS support:

1. Basic CORS Configuration in Spring Security

The simplest way to enable CORS in Spring Security is by configuring a global CORS mapping in the Spring configuration. You can define the CORS mappings to allow specific HTTP methods and domains.

Here's an example of how to configure CORS globally:

In this example:

• addMapping("/**"): Applies the CORS policy to all endpoints.
• allowedOrigins("http://localhost:3000"): Allows requests only from http://localhost:3000.
• allowedMethods("GET", "POST", "PUT", "DELETE"): Allows only the specified HTTP methods.
• allowedHeaders("*"): Allows all HTTP headers.
• allowCredentials(true): Allows credentials such as cookies to be sent with the requests.

This configuration can be added to any Spring Boot configuration class to globally configure CORS for your application.

2. Configuring CORS with Spring Security’s HttpSecurity

In Spring Security, you also need to explicitly enable CORS in the HttpSecurity configuration to allow cross-origin requests for secured endpoints.

Here’s an example of how to configure CORS in the Spring Security configuration class:

In this example:

• http.cors(): This enables CORS in Spring Security, applying the CORS mappings that were defined globally.
• authorizeRequests(): This secures other endpoints and allows public access to /public/**.

3. Using a Custom CORS Filter

If you need more control over the CORS configuration, you can implement a custom filter to handle CORS requests.

In this example:

• A CorsConfiguration object is created and customized with specific CORS settings.
• The UrlBasedCorsConfigurationSource maps the configuration to all URLs (/**).
• A CorsFilter is returned as a bean to handle the CORS logic.

4. Enabling CORS for Specific Endpoints

If you want to configure CORS for specific URLs rather than globally, you can configure the CORS mappings to be more restrictive. Here’s how to apply it only to specific endpoints:

In this case, only requests to endpoints starting with /api/** are affected by the CORS configuration, allowing you to restrict which resources can be accessed cross-origin.

Practical Examples of CORS Configuration

Example 1: Allowing All Origins for Public APIs

If your API is open to any domain (e.g., public REST APIs), you can configure CORS to allow all origins.

Example 2: Restricting CORS to Specific Domains

For added security, you may want to restrict CORS requests to specific domains. For example, allowing requests only from https://myfrontend.com:

Conclusion

Configuring CORS in Spring Security is essential when building applications that need to support cross-origin requests, such as when your frontend and backend are hosted on different domains. Spring Security provides multiple ways to configure CORS, including global settings, HTTP security configuration, and custom filters. By carefully configuring CORS, you can ensure that your application is both secure and functional when dealing with cross-origin requests.