diff --git a/config/src/main/java/org/springframework/security/config/web/server/ServerHttpSecurity.java b/config/src/main/java/org/springframework/security/config/web/server/ServerHttpSecurity.java
index 188b9d761a..15d05aa732 100644
--- a/config/src/main/java/org/springframework/security/config/web/server/ServerHttpSecurity.java
+++ b/config/src/main/java/org/springframework/security/config/web/server/ServerHttpSecurity.java
@@ -714,11 +714,23 @@ public class ServerHttpSecurity {
 		 * Configures JWT Resource Server Support
 		 */
 		public class JwtSpec {
+			private ReactiveAuthenticationManager authenticationManager;
 			private ReactiveJwtDecoder jwtDecoder;
 
 			private BearerTokenServerWebExchangeMatcher bearerTokenServerWebExchangeMatcher =
 					new BearerTokenServerWebExchangeMatcher();
 
+			/**
+			 * Configures the {@link ReactiveAuthenticationManager} to use
+			 * @param authenticationManager the authentication manager to use
+			 * @return the {@code JwtSpec} for additional configuration
+			 */
+			public JwtSpec authenticationManager(ReactiveAuthenticationManager authenticationManager) {
+				Assert.notNull(authenticationManager, "authenticationManager cannot be null");
+				this.authenticationManager = authenticationManager;
+				return this;
+			}
+
 			/**
 			 * Configures the {@link ReactiveJwtDecoder} to use
 			 * @param jwtDecoder the decoder to use
@@ -764,9 +776,7 @@ public class ServerHttpSecurity {
 				registerDefaultAuthenticationEntryPoint(http);
 				registerDefaultCsrfOverride(http);
 
-				ReactiveJwtDecoder jwtDecoder = getJwtDecoder();
-				JwtReactiveAuthenticationManager authenticationManager = new JwtReactiveAuthenticationManager(
-						jwtDecoder);
+				ReactiveAuthenticationManager authenticationManager = getAuthenticationManager();
 				AuthenticationWebFilter oauth2 = new AuthenticationWebFilter(authenticationManager);
 				oauth2.setServerAuthenticationConverter(bearerTokenConverter);
 				oauth2.setAuthenticationFailureHandler(new ServerAuthenticationEntryPointFailureHandler(entryPoint));
@@ -782,6 +792,17 @@ public class ServerHttpSecurity {
 				return this.jwtDecoder;
 			}
 
+			private ReactiveAuthenticationManager getAuthenticationManager() {
+				if (this.authenticationManager != null) {
+					return this.authenticationManager;
+				}
+
+				ReactiveJwtDecoder jwtDecoder = getJwtDecoder();
+				ReactiveAuthenticationManager authenticationManager =
+						new JwtReactiveAuthenticationManager(jwtDecoder);
+				return authenticationManager;
+			}
+
 			private void registerDefaultAccessDeniedHandler(ServerHttpSecurity http) {
 				if ( http.exceptionHandling != null ) {
 					http.defaultAccessDeniedHandlers.add(
@@ -794,7 +815,7 @@ public class ServerHttpSecurity {
 			}
 
 			private void registerDefaultAuthenticationEntryPoint(ServerHttpSecurity http) {
-				if ( http.exceptionHandling != null ) {
+				if (http.exceptionHandling != null) {
 					http.defaultEntryPoints.add(
 							new DelegateEntry(
 									this.bearerTokenServerWebExchangeMatcher,
diff --git a/config/src/test/java/org/springframework/security/config/web/server/OAuth2ResourceServerSpecTests.java b/config/src/test/java/org/springframework/security/config/web/server/OAuth2ResourceServerSpecTests.java
index b3e99f2981..534c4bd866 100644
--- a/config/src/test/java/org/springframework/security/config/web/server/OAuth2ResourceServerSpecTests.java
+++ b/config/src/test/java/org/springframework/security/config/web/server/OAuth2ResourceServerSpecTests.java
@@ -39,8 +39,12 @@ import org.springframework.beans.factory.NoUniqueBeanDefinitionException;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.ApplicationContext;
 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.test.SpringTestRule;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.oauth2.core.OAuth2AuthenticationException;
+import org.springframework.security.oauth2.core.OAuth2Error;
 import org.springframework.security.oauth2.jose.jws.JwsAlgorithms;
 import org.springframework.security.oauth2.jwt.Jwt;
 import org.springframework.security.oauth2.jwt.ReactiveJwtDecoder;
@@ -57,6 +61,7 @@ import org.springframework.web.reactive.config.EnableWebFlux;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatCode;
 import static org.hamcrest.core.StringStartsWith.startsWith;
+import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.verify;
@@ -161,6 +166,23 @@ public class OAuth2ResourceServerSpecTests {
 				.expectStatus().isOk();
 	}
 
+
+	@Test
+	public void getWhenUsingCustomAuthenticationManagerThenUsesItAccordingly() {
+		this.spring.register(CustomAuthenticationManagerConfig.class).autowire();
+
+		ReactiveAuthenticationManager authenticationManager = this.spring.getContext().getBean(
+				ReactiveAuthenticationManager.class);
+		when(authenticationManager.authenticate(any(Authentication.class)))
+				.thenReturn(Mono.error(new OAuth2AuthenticationException(new OAuth2Error("mock-failure"))));
+
+		this.client.get()
+				.headers(headers -> headers.setBearerAuth(this.messageReadToken))
+				.exchange()
+				.expectStatus().isUnauthorized()
+				.expectHeader().value(HttpHeaders.WWW_AUTHENTICATE, startsWith("Bearer error=\"mock-failure\""));
+	}
+
 	@Test
 	public void postWhenSignedThenReturnsOk() {
 		this.spring.register(PublicKeyConfig.class, RootController.class).autowire();
@@ -343,6 +365,27 @@ public class OAuth2ResourceServerSpecTests {
 		}
 	}
 
+	@EnableWebFlux
+	@EnableWebFluxSecurity
+	static class CustomAuthenticationManagerConfig {
+		@Bean
+		SecurityWebFilterChain springSecurity(ServerHttpSecurity http) {
+			// @formatter:off
+			http
+				.oauth2ResourceServer()
+					.jwt()
+						.authenticationManager(authenticationManager());
+			// @formatter:on
+
+			return http.build();
+		}
+
+		@Bean
+		ReactiveAuthenticationManager authenticationManager() {
+			return mock(ReactiveAuthenticationManager.class);
+		}
+	}
+
 	@RestController
 	static class RootController {
 		@GetMapping
@@ -356,7 +399,6 @@ public class OAuth2ResourceServerSpecTests {
 		}
 	}
 
-
 	private static RSAPublicKey publicKey() throws NoSuchAlgorithmException, InvalidKeySpecException {
 		String modulus = "26323220897278656456354815752829448539647589990395639665273015355787577386000316054335559633864476469390247312823732994485311378484154955583861993455004584140858982659817218753831620205191028763754231454775026027780771426040997832758235764611119743390612035457533732596799927628476322029280486807310749948064176545712270582940917249337311592011920620009965129181413510845780806191965771671528886508636605814099711121026468495328702234901200169245493126030184941412539949521815665744267183140084667383643755535107759061065656273783542590997725982989978433493861515415520051342321336460543070448417126615154138673620797";
 		String exponent = "65537";