Similar to Servlet X.509 authentication, the reactive x509 authentication filter allows extracting an authentication token from a certificate provided by a client.spring-doc.cn

The following example shows a reactive x509 security configuration:spring-doc.cn

@Bean
public SecurityWebFilterChain securityWebFilterChain(ServerHttpSecurity http) {
	http
		.x509(withDefaults())
		.authorizeExchange(exchanges -> exchanges
		    .anyExchange().permitAll()
		);
	return http.build();
}
@Bean
fun securityWebFilterChain(http: ServerHttpSecurity): SecurityWebFilterChain {
    return http {
        x509 { }
        authorizeExchange {
            authorize(anyExchange, authenticated)
        }
    }
}

In the preceding configuration, when neither principalExtractor nor authenticationManager is provided, defaults are 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 a user account with a name extracted by principalExtractor exists and that it is not locked, disabled, or expired.spring-doc.cn

The following example demonstrates how these defaults can be overridden:spring-doc.cn

@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();
}
@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 the previous 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 is authenticated.spring-doc.cn

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