[[reactive-x509]]
= Reactive X.509 Authentication

Similar to xref:servlet/authentication/x509.adoc#servlet-x509[Servlet X.509 authentication], reactive x509 authentication filter allows extracting an authentication token from a certificate provided by a client.

Below is an example of a reactive x509 security configuration:
====
.Java
[source,java,role="primary"]
----
@Bean
public SecurityWebFilterChain securityWebFilterChain(ServerHttpSecurity http) {
	http
		.x509(withDefaults())
		.authorizeExchange(exchanges -> exchanges
		    .anyExchange().permitAll()
		);
	return http.build();
}
----

.Kotlin
[source,kotlin,role="secondary"]
----
@Bean
fun securityWebFilterChain(http: ServerHttpSecurity): SecurityWebFilterChain {
    return http {
        x509 { }
        authorizeExchange {
            authorize(anyExchange, authenticated)
        }
    }
}
----
====

In the configuration above, when neither `principalExtractor` nor `authenticationManager` is provided defaults will be used. The default principal extractor is `SubjectDnX509PrincipalExtractor` which extracts the CN (common name) field from a certificate provided by a client. The default authentication manager is `ReactivePreAuthenticatedAuthenticationManager` which performs user account validation, checking that user account with a name extracted by `principalExtractor` exists and it is not locked, disabled, or expired.

The next example demonstrates how these defaults can be overridden.

====
.Java
[source,java,role="primary"]
----
@Bean
public SecurityWebFilterChain securityWebFilterChain(ServerHttpSecurity http) {
	SubjectDnX509PrincipalExtractor principalExtractor =
	        new SubjectDnX509PrincipalExtractor();

	principalExtractor.setSubjectDnRegex("OU=(.*?)(?:,|$)");

	ReactiveAuthenticationManager authenticationManager = authentication -> {
		authentication.setAuthenticated("Trusted Org Unit".equals(authentication.getName()));
		return Mono.just(authentication);
	};

	http
		.x509(x509 -> x509
		    .principalExtractor(principalExtractor)
		    .authenticationManager(authenticationManager)
		)
		.authorizeExchange(exchanges -> exchanges
		    .anyExchange().authenticated()
		);
	return http.build();
}
----

.Kotlin
[source,kotlin,role="secondary"]
----
@Bean
fun securityWebFilterChain(http: ServerHttpSecurity): SecurityWebFilterChain? {
    val customPrincipalExtractor = SubjectDnX509PrincipalExtractor()
    customPrincipalExtractor.setSubjectDnRegex("OU=(.*?)(?:,|$)")
    val customAuthenticationManager = ReactiveAuthenticationManager { authentication: Authentication ->
        authentication.isAuthenticated = "Trusted Org Unit" == authentication.name
        Mono.just(authentication)
    }
    return http {
        x509 {
            principalExtractor = customPrincipalExtractor
            authenticationManager = customAuthenticationManager
        }
        authorizeExchange {
            authorize(anyExchange, authenticated)
        }
    }
}
----
====

In this example, a username is extracted from the OU field of a client certificate instead of CN, and account lookup using `ReactiveUserDetailsService` is not performed at all. Instead, if the provided certificate issued to an OU named "Trusted Org Unit", a request will be authenticated.

For an example of configuring Netty and `WebClient` or `curl` command-line tool to use mutual TLS and enable X.509 authentication, please refer to https://github.com/spring-projects/spring-security-samples/tree/main/servlet/java-configuration/authentication/x509.