[[jc-erms]]
= EnableReactiveMethodSecurity

Spring Security supports method security using https://projectreactor.io/docs/core/release/reference/#context[Reactor's Context] which is setup using `ReactiveSecurityContextHolder`.
For example, this demonstrates how to retrieve the currently logged in user's message.

[NOTE]
====
For this to work the return type of the method must be a `org.reactivestreams.Publisher` (i.e. `Mono`/`Flux`).
This is necessary to integrate with Reactor's `Context`.
====

[source,java]
----
Authentication authentication = new TestingAuthenticationToken("user", "password", "ROLE_USER");

Mono<String> messageByUsername = ReactiveSecurityContextHolder.getContext()
	.map(SecurityContext::getAuthentication)
	.map(Authentication::getName)
	.flatMap(this::findMessageByUsername)
	// In a WebFlux application the `subscriberContext` is automatically setup using `ReactorContextWebFilter`
	.subscriberContext(ReactiveSecurityContextHolder.withAuthentication(authentication));

StepVerifier.create(messageByUsername)
	.expectNext("Hi user")
	.verifyComplete();
----

with `this::findMessageByUsername` defined as:

[source,java]
----
Mono<String> findMessageByUsername(String username) {
	return Mono.just("Hi " + username);
}
----

Below is a minimal method security configuration when using method security in reactive applications.

[source,java]
----
@EnableReactiveMethodSecurity
public class SecurityConfig {
	@Bean
	public MapReactiveUserDetailsService userDetailsService() {
		User.UserBuilder userBuilder = User.withDefaultPasswordEncoder();
		UserDetails rob = userBuilder.username("rob")
			.password("rob")
			.roles("USER")
			.build();
		UserDetails admin = userBuilder.username("admin")
			.password("admin")
			.roles("USER","ADMIN")
			.build();
		return new MapReactiveUserDetailsService(rob, admin);
	}
}
----

Consider the following class:

[source,java]
----
@Component
public class HelloWorldMessageService {
	@PreAuthorize("hasRole('ADMIN')")
	public Mono<String> findMessage() {
		return Mono.just("Hello World!");
	}
}
----

Combined with our configuration above, `@PreAuthorize("hasRole('ADMIN')")` will ensure that `findByMessage` is only invoked by a user with the role `ADMIN`.
It is important to note that any of the expressions in standard method security work for `@EnableReactiveMethodSecurity`.
However, at this time we only support return type of `Boolean` or `boolean` of the expression.
This means that the expression must not block.

When integrating with <<jc-webflux>>, the Reactor Context is automatically established by Spring Security according to the authenticated user.

[source,java]
----
@EnableWebFluxSecurity
@EnableReactiveMethodSecurity
public class SecurityConfig {

	@Bean
	SecurityWebFilterChain springWebFilterChain(ServerHttpSecurity http) throws Exception {
		return http
			// Demonstrate that method security works
			// Best practice to use both for defense in depth
			.authorizeExchange(exchanges -> exchanges
				.anyExchange().permitAll()
			)
			.httpBasic(withDefaults())
			.build();
	}

	@Bean
	MapReactiveUserDetailsService userDetailsService() {
		User.UserBuilder userBuilder = User.withDefaultPasswordEncoder();
		UserDetails rob = userBuilder.username("rob")
			.password("rob")
			.roles("USER")
			.build();
		UserDetails admin = userBuilder.username("admin")
			.password("admin")
			.roles("USER","ADMIN")
			.build();
		return new MapReactiveUserDetailsService(rob, admin);
	}
}

----

You can find a complete sample in {gh-samples-url}/javaconfig/hellowebflux-method[hellowebflux-method]
