[[jc-erms]]
= EnableReactiveMethodSecurity

Spring Security supports method security by using https://projectreactor.io/docs/core/release/reference/#context[Reactor's Context], which is set up by `ReactiveSecurityContextHolder`.
The following example shows how to retrieve the currently logged in user's message:

[NOTE]
====
For this example to work, the return type of the method must be a `org.reactivestreams.Publisher` (that is, a `Mono` or a `Flux`) or the function must be a Kotlin coroutine function.
This is necessary to integrate with Reactor's `Context`.
====

====
.Java
[source,java,role="primary"]
----
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`
	.contextWrite(ReactiveSecurityContextHolder.withAuthentication(authentication));

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

.Kotlin
[source,kotlin,role="secondary"]
----
val authentication: Authentication = TestingAuthenticationToken("user", "password", "ROLE_USER")

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

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

Where `this::findMessageByUsername` is defined as:

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

.Kotlin
[source,kotlin,role="secondary"]
----
fun findMessageByUsername(username: String): Mono<String> {
	return Mono.just("Hi $username")
}
----
====

The following minimal method security configures method security in reactive applications:

====
.Java
[source,java,role="primary"]
----
@Configuration
@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);
	}
}
----

.Kotlin
[source,kotlin,role="secondary"]
----
@Configuration
@EnableReactiveMethodSecurity
class SecurityConfig {
	@Bean
	fun userDetailsService(): MapReactiveUserDetailsService {
		val userBuilder: User.UserBuilder = User.withDefaultPasswordEncoder()
		val rob = userBuilder.username("rob")
			.password("rob")
			.roles("USER")
			.build()
		val admin = userBuilder.username("admin")
			.password("admin")
			.roles("USER", "ADMIN")
			.build()
		return MapReactiveUserDetailsService(rob, admin)
	}
}
----
====

Consider the following class:

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

.Kotlin
[source,kotlin,role="secondary"]
----
@Component
class HelloWorldMessageService {
	@PreAuthorize("hasRole('ADMIN')")
	fun findMessage(): Mono<String> {
		return Mono.just("Hello World!")
	}
}
----
====

Alternatively, the following class uses Kotlin coroutines:

====
.Kotlin
[source,kotlin,role="primary"]
----
@Component
class HelloWorldMessageService {
    @PreAuthorize("hasRole('ADMIN')")
    suspend fun findMessage(): String {
        delay(10)
        return "Hello World!"
    }
}
----
====


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

When integrating with xref:reactive/configuration/webflux.adoc#jc-webflux[WebFlux Security], the Reactor Context is automatically established by Spring Security according to the authenticated user:

====
.Java
[source,java,role="primary"]
----
@Configuration
@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);
	}
}
----

.Kotlin
[source,kotlin,role="secondary"]
----
@Configuration
@EnableWebFluxSecurity
@EnableReactiveMethodSecurity
class SecurityConfig {
	@Bean
	open fun springWebFilterChain(http: ServerHttpSecurity): SecurityWebFilterChain {
		return http {
			authorizeExchange {
				authorize(anyExchange, permitAll)
			}
			httpBasic { }
		}
	}

	@Bean
	fun userDetailsService(): MapReactiveUserDetailsService {
		val userBuilder: User.UserBuilder = User.withDefaultPasswordEncoder()
		val rob = userBuilder.username("rob")
			.password("rob")
			.roles("USER")
			.build()
		val admin = userBuilder.username("admin")
			.password("admin")
			.roles("USER", "ADMIN")
			.build()
		return MapReactiveUserDetailsService(rob, admin)
	}
}
----
====

You can find a complete sample in {gh-samples-url}/reactive/webflux/java/method[hellowebflux-method].