[[cors]]
= CORS

Spring Framework provides https://docs.spring.io/spring/docs/current/spring-framework-reference/web.html#mvc-cors[first class support for CORS].
CORS must be processed before Spring Security, because the pre-flight request does not contain any cookies (that is, the `JSESSIONID`).
If the request does not contain any cookies and Spring Security is first, the request determines that the user is not authenticated (since there are no cookies in the request) and rejects it.

The easiest way to ensure that CORS is handled first is to use the `CorsFilter`.
Users can integrate the `CorsFilter` with Spring Security by providing a `CorsConfigurationSource` that uses the following:

====
.Java
[source,java,role="primary"]
----
@Configuration
@EnableWebSecurity
public class WebSecurityConfig {

	@Bean
	public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
		http
			// by default uses a Bean by the name of corsConfigurationSource
			.cors(withDefaults())
			...
		return http.build();
	}

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

.Kotlin
[source,kotlin,role="secondary"]
----
@Configuration
@EnableWebSecurity
open class WebSecurityConfig {
    @Bean
    open fun filterChain(http: HttpSecurity): SecurityFilterChain {
        http {
            // by default uses a Bean by the name of corsConfigurationSource
            cors { }
            // ...
        }
        return http.build()
    }

    @Bean
    open fun corsConfigurationSource(): CorsConfigurationSource {
        val configuration = CorsConfiguration()
        configuration.allowedOrigins = listOf("https://example.com")
        configuration.allowedMethods = listOf("GET", "POST")
        val source = UrlBasedCorsConfigurationSource()
        source.registerCorsConfiguration("/**", configuration)
        return source
    }
}
----
====

The following listing does the same thing in XML:

====
[source,xml]
----
<http>
	<cors configuration-source-ref="corsSource"/>
	...
</http>
<b:bean id="corsSource" class="org.springframework.web.cors.UrlBasedCorsConfigurationSource">
	...
</b:bean>
----
====

If you use Spring MVC's CORS support, you can omit specifying the `CorsConfigurationSource` and Spring Security uses the CORS configuration provided to Spring MVC:

====
.Java
[source,java,role="primary"]
----
@Configuration
@EnableWebSecurity
public class WebSecurityConfig {

	@Bean
	public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
		http
			// if Spring MVC is on classpath and no CorsConfigurationSource is provided,
			// Spring Security will use CORS configuration provided to Spring MVC
			.cors(withDefaults())
			...
		return http.build();
	}
}
----

.Kotlin
[source,kotlin,role="secondary"]
----
@Configuration
@EnableWebSecurity
open class WebSecurityConfig {
    @Bean
    open fun filterChain(http: HttpSecurity): SecurityFilterChain {
        http {
            // if Spring MVC is on classpath and no CorsConfigurationSource is provided,
            // Spring Security will use CORS configuration provided to Spring MVC
            cors { }
            // ...
        }
        return http.build()
    }
}
----
====

The following listing does the same thing in XML:

====
[source,xml]
----
<http>
	<!-- Default to Spring MVC's CORS configuration -->
	<cors />
	...
</http>
----
====
