[[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`. Note that Spring Security will automatically configure CORS only if a `UrlBasedCorsConfigurationSource` instance is present.
For example, the following will integrate CORS support within Spring Security:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Bean
UrlBasedCorsConfigurationSource 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"]
----
@Bean
fun corsConfigurationSource(): UrlBasedCorsConfigurationSource {
    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:

[tabs]
======
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>
----

If you have more than one `CorsConfigurationSource` bean, Spring Security won't automatically configure CORS support for you, that is because it cannot decide which one to use.
If you want to specify different `CorsConfigurationSource` for each `SecurityFilterChain`, you can pass it directly into the `.cors()` DSL.

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

	@Bean
	@Order(0)
	public SecurityFilterChain apiFilterChain(HttpSecurity http) throws Exception {
		http
			.securityMatcher("/api/**")
			.cors((cors) -> cors
				.configurationSource(apiConfigurationSource())
			)
			...
		return http.build();
	}

	@Bean
	@Order(1)
	public SecurityFilterChain myOtherFilterChain(HttpSecurity http) throws Exception {
		http
			.cors((cors) -> cors
				.configurationSource(myWebsiteConfigurationSource())
			)
			...
		return http.build();
	}

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

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

[WARNING]
====
CORS is a browser-based security feature.
By disabling CORS in Spring Security with `.cors(CorsConfigurer::disable)`, you are not removing CORS protection from your browser.
Instead, you are removing CORS support from Spring Security, and users will not be able to interact with your Spring backend from a cross-origin browser application.
To fix CORS errors in your application, you must enable CORS support, and provide an appropriate configuration source.
====
