diff --git a/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/security/reactive/ReactiveManagementWebSecurityAutoConfiguration.java b/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/security/reactive/ReactiveManagementWebSecurityAutoConfiguration.java
index 7ceff512875..a1c4a600fe9 100644
--- a/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/security/reactive/ReactiveManagementWebSecurityAutoConfiguration.java
+++ b/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/security/reactive/ReactiveManagementWebSecurityAutoConfiguration.java
@@ -16,6 +16,8 @@
 
 package org.springframework.boot.actuate.autoconfigure.security.reactive;
 
+import reactor.core.publisher.Mono;
+
 import org.springframework.boot.actuate.autoconfigure.endpoint.web.WebEndpointAutoConfiguration;
 import org.springframework.boot.actuate.autoconfigure.health.HealthEndpointAutoConfiguration;
 import org.springframework.boot.actuate.autoconfigure.info.InfoEndpointAutoConfiguration;
@@ -28,10 +30,14 @@ import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplicat
 import org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration;
 import org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration;
 import org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration;
+import org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration;
 import org.springframework.context.annotation.Bean;
+import org.springframework.security.authentication.ReactiveAuthenticationManager;
 import org.springframework.security.config.annotation.web.reactive.EnableWebFluxSecurity;
 import org.springframework.security.config.web.server.SecurityWebFiltersOrder;
 import org.springframework.security.config.web.server.ServerHttpSecurity;
+import org.springframework.security.core.userdetails.ReactiveUserDetailsService;
+import org.springframework.security.core.userdetails.UsernameNotFoundException;
 import org.springframework.security.web.server.SecurityWebFilterChain;
 import org.springframework.security.web.server.WebFilterChainProxy;
 import org.springframework.web.cors.reactive.PreFlightRequestHandler;
@@ -50,7 +56,8 @@ import static org.springframework.security.config.Customizer.withDefaults;
 @AutoConfiguration(before = ReactiveSecurityAutoConfiguration.class,
 		after = { HealthEndpointAutoConfiguration.class, InfoEndpointAutoConfiguration.class,
 				WebEndpointAutoConfiguration.class, ReactiveOAuth2ClientAutoConfiguration.class,
-				ReactiveOAuth2ResourceServerAutoConfiguration.class })
+				ReactiveOAuth2ResourceServerAutoConfiguration.class,
+				ReactiveUserDetailsServiceAutoConfiguration.class })
 @ConditionalOnClass({ EnableWebFluxSecurity.class, WebFilterChainProxy.class })
 @ConditionalOnMissingBean({ SecurityWebFilterChain.class, WebFilterChainProxy.class })
 @ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.REACTIVE)
@@ -69,4 +76,10 @@ public class ReactiveManagementWebSecurityAutoConfiguration {
 		return http.build();
 	}
 
+	@Bean
+	@ConditionalOnMissingBean({ ReactiveAuthenticationManager.class, ReactiveUserDetailsService.class })
+	ReactiveAuthenticationManager denyAllAuthenticationManager() {
+		return (authentication) -> Mono.error(new UsernameNotFoundException(authentication.getName()));
+	}
+
 }
diff --git a/spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/security/reactive/ReactiveManagementWebSecurityAutoConfigurationTests.java b/spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/security/reactive/ReactiveManagementWebSecurityAutoConfigurationTests.java
index e41082b893a..66b39ded5a7 100644
--- a/spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/security/reactive/ReactiveManagementWebSecurityAutoConfigurationTests.java
+++ b/spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/security/reactive/ReactiveManagementWebSecurityAutoConfigurationTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -71,17 +71,26 @@ class ReactiveManagementWebSecurityAutoConfigurationTests {
 				HealthEndpointAutoConfiguration.class, InfoEndpointAutoConfiguration.class,
 				WebFluxAutoConfiguration.class, EnvironmentEndpointAutoConfiguration.class,
 				EndpointAutoConfiguration.class, WebEndpointAutoConfiguration.class,
-				ReactiveSecurityAutoConfiguration.class, ReactiveManagementWebSecurityAutoConfiguration.class))
-		.withUserConfiguration(UserDetailsServiceConfiguration.class);
+				ReactiveSecurityAutoConfiguration.class, ReactiveManagementWebSecurityAutoConfiguration.class));
 
 	@Test
 	void permitAllForHealth() {
-		this.contextRunner.run((context) -> assertThat(getAuthenticateHeader(context, "/actuator/health")).isNull());
+		this.contextRunner.withUserConfiguration(UserDetailsServiceConfiguration.class)
+			.run((context) -> assertThat(getAuthenticateHeader(context, "/actuator/health")).isNull());
 	}
 
 	@Test
 	void securesEverythingElse() {
+		this.contextRunner.withUserConfiguration(UserDetailsServiceConfiguration.class).run((context) -> {
+			assertThat(getAuthenticateHeader(context, "/actuator").get(0)).contains("Basic realm=");
+			assertThat(getAuthenticateHeader(context, "/foo").toString()).contains("Basic realm=");
+		});
+	}
+
+	@Test
+	void noExistingAuthenticationManagerOrUserDetailsService() {
 		this.contextRunner.run((context) -> {
+			assertThat(getAuthenticateHeader(context, "/actuator/health")).isNull();
 			assertThat(getAuthenticateHeader(context, "/actuator").get(0)).contains("Basic realm=");
 			assertThat(getAuthenticateHeader(context, "/foo").toString()).contains("Basic realm=");
 		});
@@ -89,10 +98,12 @@ class ReactiveManagementWebSecurityAutoConfigurationTests {
 
 	@Test
 	void usesMatchersBasedOffConfiguredActuatorBasePath() {
-		this.contextRunner.withPropertyValues("management.endpoints.web.base-path=/").run((context) -> {
-			assertThat(getAuthenticateHeader(context, "/health")).isNull();
-			assertThat(getAuthenticateHeader(context, "/foo").get(0)).contains("Basic realm=");
-		});
+		this.contextRunner.withUserConfiguration(UserDetailsServiceConfiguration.class)
+			.withPropertyValues("management.endpoints.web.base-path=/")
+			.run((context) -> {
+				assertThat(getAuthenticateHeader(context, "/health")).isNull();
+				assertThat(getAuthenticateHeader(context, "/foo").get(0)).contains("Basic realm=");
+			});
 	}
 
 	@Test
@@ -180,6 +191,11 @@ class ReactiveManagementWebSecurityAutoConfigurationTests {
 			return http.build();
 		}
 
+		@Bean
+		ReactiveAuthenticationManager authenticationManager() {
+			return mock(ReactiveAuthenticationManager.class);
+		}
+
 	}
 
 	@Configuration(proxyBeanMethods = false)