Dispose default Scheduler

AbstractUserDetailsReactiveAuthenticationManager creates parallel
Scheduler with daemon=false Threads. It is recommended to dispose such
Schedulers to be able exit the VM

Fixes gh-7492

core/src/main/java/org/springframework/security/authentication/AbstractUserDetailsReactiveAuthenticationManager.java

@@ -18,6 +18,7 @@ package org.springframework.security.authentication;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.springframework.beans.factory.DisposableBean;
 import reactor.core.publisher.Mono;
 import reactor.core.scheduler.Scheduler;
 import reactor.core.scheduler.Schedulers;
@@ -45,7 +46,7 @@ import org.springframework.util.Assert;
  * @author Eddú Meléndez
  * @since 5.2
  */
-public abstract class AbstractUserDetailsReactiveAuthenticationManager implements ReactiveAuthenticationManager {
+public abstract class AbstractUserDetailsReactiveAuthenticationManager implements ReactiveAuthenticationManager, DisposableBean {
 
 	protected final Log logger = LogFactory.getLog(getClass());
 
@@ -55,7 +56,8 @@ public abstract class AbstractUserDetailsReactiveAuthenticationManager implement
 
 	private ReactiveUserDetailsPasswordService userDetailsPasswordService;
 
-	private Scheduler scheduler = Schedulers.newParallel("password-encoder");
+	Scheduler scheduler = Schedulers.newParallel("password-encoder");
+	private boolean defaultScheduler = true;
 
 	private UserDetailsChecker preAuthenticationChecks = user -> {
 		if (!user.isAccountNonLocked()) {
@@ -138,6 +140,10 @@ public abstract class AbstractUserDetailsReactiveAuthenticationManager implement
 	 */
 	public void setScheduler(Scheduler scheduler) {
 		Assert.notNull(scheduler, "scheduler cannot be null");
+		if (this.defaultScheduler) {
+			this.defaultScheduler = false;
+			this.scheduler.dispose();
+		}
 		this.scheduler = scheduler;
 	}
 
@@ -171,4 +177,10 @@ public abstract class AbstractUserDetailsReactiveAuthenticationManager implement
 	 */
 	protected abstract Mono<UserDetails> retrieveUser(String username);
 
+	@Override
+	public void destroy() {
+		if (this.defaultScheduler) {
+			this.scheduler.dispose();
+		}
+	}
 }

core/src/test/java/org/springframework/security/authentication/ReactiveUserDetailsServiceAuthenticationManagerTests.java

@@ -33,6 +33,8 @@ import org.springframework.security.core.userdetails.ReactiveUserDetailsService;
 import org.springframework.security.core.userdetails.UserDetails;
 import org.springframework.security.crypto.password.PasswordEncoder;
 import reactor.core.publisher.Mono;
+import reactor.core.scheduler.Scheduler;
+import reactor.core.scheduler.Schedulers;
 import reactor.test.StepVerifier;
 
 /**
@@ -136,4 +138,33 @@ public class ReactiveUserDetailsServiceAuthenticationManagerTests {
 			.expectError(BadCredentialsException.class)
 			.verify();
 	}
+
+	@Test
+	public void destroyWhenDefaultSchedulerThenShouldDispose() {
+		assertThat(manager.scheduler.isDisposed()).isFalse();
+		manager.destroy();
+		assertThat(manager.scheduler.isDisposed())
+				.as("default Scheduler should be disposed")
+				.isTrue();
+	}
+
+	@Test
+	public void destroyWhenCustomSchedulerThenShouldNotDispose() {
+		manager.setScheduler(Schedulers.parallel());
+		manager.destroy();
+		assertThat(manager.scheduler.isDisposed())
+				.as("custom Scheduler should not be disposed")
+				.isFalse();
+	}
+
+	@Test
+	public void setSchedulerWhenSetCustomSchedulerThenDisposeDefault() {
+		Scheduler defaultScheduler = manager.scheduler;
+		assertThat(defaultScheduler.isDisposed()).isFalse();
+		manager.setScheduler(Schedulers.parallel());
+		assertThat(defaultScheduler.isDisposed())
+				.as("default Scheduler should be disposed")
+				.isTrue();
+	}
+
 }