CORS configuration in Security in Spring Boot

Introduction

CORS lets your web app ask for resources from another website safely. Configuring it in security helps control who can access your backend.

When your frontend and backend are on different domains or ports.

When you want to allow only specific websites to call your backend APIs.

When you want to prevent unauthorized websites from accessing your backend.

When building APIs that will be used by web apps hosted elsewhere.

When you want to customize allowed HTTP methods or headers for cross-origin requests.

Syntax

Spring Boot

import org.springframework.context.annotation.Bean;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.web.SecurityFilterChain;
import org.springframework.web.cors.CorsConfiguration;
import org.springframework.web.cors.UrlBasedCorsConfigurationSource;
import org.springframework.web.filter.CorsFilter;

@Bean
public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
    http.cors(cors -> cors.configurationSource(request -> {
        CorsConfiguration config = new CorsConfiguration();
        config.setAllowedOrigins(List.of("https://example.com"));
        config.setAllowedMethods(List.of("GET", "POST"));
        config.setAllowedHeaders(List.of("Authorization", "Content-Type"));
        return config;
    }))
    .authorizeHttpRequests(auth -> auth.anyRequest().authenticated());
    return http.build();
}

You define CORS rules inside the security filter chain.

Use cors.configurationSource to customize allowed origins, methods, and headers.

Examples

Allows only the specified origin and HTTP methods.

Spring Boot

http.cors(cors -> cors.configurationSource(request -> {
    CorsConfiguration config = new CorsConfiguration();
    config.setAllowedOrigins(List.of("https://myfrontend.com"));
    config.setAllowedMethods(List.of("GET", "POST", "PUT"));
    return config;
}))

Allows all origins, methods, and headers (use carefully).

Spring Boot

http.cors(cors -> cors.configurationSource(request -> {
    CorsConfiguration config = new CorsConfiguration();
    config.addAllowedOriginPattern("*");
    config.addAllowedMethod("*");
    config.addAllowedHeader("*");
    return config;
}))

Sample Program

This Spring Boot security config allows cross-origin requests only from https://trustedsite.com with GET and POST methods. It also requires authentication for all requests.

Spring Boot

package com.example.demo;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.web.SecurityFilterChain;
import org.springframework.web.cors.CorsConfiguration;
import java.util.List;

@Configuration
public class SecurityConfig {

    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        http.cors(cors -> cors.configurationSource(request -> {
            CorsConfiguration config = new CorsConfiguration();
            config.setAllowedOrigins(List.of("https://trustedsite.com"));
            config.setAllowedMethods(List.of("GET", "POST"));
            config.setAllowedHeaders(List.of("Authorization", "Content-Type"));
            return config;
        }))
        .authorizeHttpRequests(auth -> auth.anyRequest().authenticated())
        .httpBasic();
        return http.build();
    }
}

Important Notes

Always specify allowed origins explicitly to avoid security risks.

Use addAllowedOriginPattern("*") only if you understand the risks.

Test CORS settings using browser DevTools Network tab to see request headers and responses.

Summary

CORS configuration controls which websites can call your backend.

In Spring Security, configure CORS inside the security filter chain.

Always restrict origins and methods to keep your app safe.

Practice

1. What is the main purpose of configuring CORS in a Spring Boot security setup?

easy

A. To control which external websites can access your backend resources

B. To improve database query performance

C. To manage user authentication tokens

D. To style the frontend user interface

Solution

1. Step 1: Understand CORS role in web security

   CORS (Cross-Origin Resource Sharing) controls which external domains can call your backend APIs.

2. Step 2: Identify the purpose in Spring Boot security

   Configuring CORS in Spring Security allows safe cross-site requests by specifying allowed origins and methods.

3. Final Answer:

   To control which external websites can access your backend resources -> Option A

4. Quick Check:

   CORS controls access origins = A [OK]

Hint: CORS = Cross-Origin access control [OK]

Common Mistakes:

• Confusing CORS with authentication
• Thinking CORS improves database speed
• Assuming CORS styles frontend

2. Which of the following is the correct way to enable CORS in a Spring Security configuration class?

easy

A. http.corsEnabled(true);

B. http.enableCors();

C. http.allowCors(true);

D. http.cors().and().csrf().disable();

Solution

1. Step 1: Recall Spring Security CORS enabling syntax

   Spring Security uses the method http.cors() to enable CORS support.

2. Step 2: Identify the correct chaining method

   The correct chaining to disable CSRF and enable CORS is http.cors().and().csrf().disable();

3. Final Answer:

   http.cors().and().csrf().disable(); -> Option D

4. Quick Check:

   Enable CORS with http.cors() = C [OK]

Hint: Use http.cors() to enable CORS in Spring Security [OK]

Common Mistakes:

• Using non-existent methods like enableCors()
• Forgetting to chain with .and()
• Confusing CORS enabling with CSRF

3. Given this Spring Security CORS configuration snippet, what origins are allowed?

@Bean
public CorsConfigurationSource corsConfigurationSource() {
  CorsConfiguration configuration = new CorsConfiguration();
  configuration.setAllowedOrigins(List.of("https://example.com", "https://app.example.com"));
  configuration.setAllowedMethods(List.of("GET", "POST"));
  UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
  source.registerCorsConfiguration("/**", configuration);
  return source;
}

medium

A. No origins are allowed because configuration is incomplete

B. Requests from any origin are allowed

C. Only requests from https://example.com and https://app.example.com are allowed

D. Only GET requests from any origin are allowed

Solution

1. Step 1: Analyze allowed origins list

   The code sets allowed origins explicitly to "https://example.com" and "https://app.example.com".

2. Step 2: Understand effect on requests

   Only requests coming from these two origins will be accepted; others will be blocked by CORS policy.

3. Final Answer:

   Only requests from https://example.com and https://app.example.com are allowed -> Option C

4. Quick Check:

   Allowed origins = example.com and app.example.com = D [OK]

Hint: Allowed origins list controls which sites can call backend [OK]

Common Mistakes:

• Assuming all origins allowed by default
• Confusing allowed methods with allowed origins
• Thinking configuration is incomplete without headers

4. Identify the error in this Spring Security CORS configuration code:

@Bean
public CorsConfigurationSource corsConfigurationSource() {
  CorsConfiguration configuration = new CorsConfiguration();
  configuration.setAllowedOrigins("*");
  configuration.setAllowedMethods(List.of("GET", "POST"));
  UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
  source.registerCorsConfiguration("/**", configuration);
  return source;
}

medium

A. Allowed methods list is missing PUT and DELETE

B. setAllowedOrigins expects a list, not a single string

C. UrlBasedCorsConfigurationSource cannot be used here

D. The method should return void, not CorsConfigurationSource

Solution

1. Step 1: Check setAllowedOrigins parameter type

   The method setAllowedOrigins requires a List<String>, but the code passes a single String "*".

2. Step 2: Understand correct usage for wildcard

   To allow all origins, use List.of("*") instead of a plain string.

3. Final Answer:

   setAllowedOrigins expects a list, not a single string -> Option B

4. Quick Check:

   Allowed origins must be List<String> = B [OK]

Hint: setAllowedOrigins needs a list, not a string [OK]

Common Mistakes:

• Passing a string instead of a list to setAllowedOrigins
• Ignoring method parameter types
• Assuming missing HTTP methods cause errors here

5. You want to allow all origins but only GET and POST methods in your Spring Security CORS config. Which code snippet correctly achieves this while following best practices?

hard

A. configuration.setAllowedOriginPatterns(List.of("*")); configuration.setAllowedMethods(List.of("GET", "POST"));

B. configuration.setAllowedOrigins(List.of("*")); configuration.setAllowedMethods(List.of("GET", "POST"));

C. configuration.setAllowedOrigins("*"); configuration.setAllowedMethods(List.of("GET", "POST"));

D. configuration.setAllowedOrigins(List.of("*")); configuration.setAllowedMethods(List.of("GET", "POST", "PUT"));

Solution

1. Step 1: Understand wildcard origin allowance

   Using setAllowedOrigins(List.of("*")) is deprecated and may cause issues; instead, setAllowedOriginPatterns supports wildcards properly.

2. Step 2: Check allowed methods correctness

   Only GET and POST methods are allowed as required.

3. Final Answer:

   configuration.setAllowedOriginPatterns(List.of("*")); configuration.setAllowedMethods(List.of("GET", "POST")); -> Option A

4. Quick Check:

   Use allowedOriginPatterns for wildcard origins = A [OK]

Hint: Use setAllowedOriginPatterns for wildcard origins [OK]

Common Mistakes:

• Using setAllowedOrigins with "*" string
• Allowing extra HTTP methods by mistake
• Passing string instead of list to allowed origins