Allow customization of underlying ClientHttpRequestFactory components

Update `ClientHttpRequestFactoryBuilder` implementations for
`HttpComponents`, `Jdk`, `Jetty` and `Reactor` to allow customization
of the underlying components.

Closes gh-39035

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/http/client/AbstractClientHttpRequestFactoryBuilder.java

@@ -35,12 +35,20 @@ import org.springframework.util.Assert;
 abstract class AbstractClientHttpRequestFactoryBuilder<T extends ClientHttpRequestFactory>
 		implements ClientHttpRequestFactoryBuilder<T> {
 
+	private static final Consumer<?> EMPTY_CUSTOMIZER = (t) -> {
+	};
+
 	private final List<Consumer<T>> customizers;
 
 	protected AbstractClientHttpRequestFactoryBuilder(List<Consumer<T>> customizers) {
 		this.customizers = (customizers != null) ? customizers : Collections.emptyList();
 	}
 
+	@SuppressWarnings("unchecked")
+	protected static <T> Consumer<T> emptyCustomizer() {
+		return (Consumer<T>) EMPTY_CUSTOMIZER;
+	}
+
 	protected final List<Consumer<T>> getCustomizers() {
 		return this.customizers;
 	}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/http/client/HttpComponentsClientHttpRequestFactoryBuilder.java

@@ -23,6 +23,7 @@ import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Consumer;
+import java.util.function.Function;
 
 import org.apache.hc.client5.http.classic.HttpClient;
 import org.apache.hc.client5.http.impl.DefaultRedirectStrategy;
@@ -32,6 +33,7 @@ import org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManagerBuil
 import org.apache.hc.client5.http.protocol.RedirectStrategy;
 import org.apache.hc.client5.http.ssl.DefaultClientTlsStrategy;
 import org.apache.hc.client5.http.ssl.DefaultHostnameVerifier;
+import org.apache.hc.client5.http.ssl.TlsSocketStrategy;
 import org.apache.hc.core5.http.HttpRequest;
 import org.apache.hc.core5.http.HttpResponse;
 import org.apache.hc.core5.http.io.SocketConfig;
@@ -42,6 +44,7 @@ import org.springframework.boot.http.client.ClientHttpRequestFactorySettings.Red
 import org.springframework.boot.ssl.SslBundle;
 import org.springframework.boot.ssl.SslOptions;
 import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
+import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 
 /**
@@ -55,25 +58,104 @@ import org.springframework.util.ClassUtils;
 public final class HttpComponentsClientHttpRequestFactoryBuilder
 		extends AbstractClientHttpRequestFactoryBuilder<HttpComponentsClientHttpRequestFactory> {
 
+	private final Consumer<HttpClientBuilder> httpClientCustomizer;
+
+	private final Consumer<PoolingHttpClientConnectionManagerBuilder> connectionManagerCustomizer;
+
+	private final Consumer<SocketConfig.Builder> socketConfigCustomizer;
+
+	private final Function<SslBundle, TlsSocketStrategy> tlsSocketStrategyFactory;
+
 	HttpComponentsClientHttpRequestFactoryBuilder() {
-		this(Collections.emptyList());
+		this(Collections.emptyList(), emptyCustomizer(), emptyCustomizer(), emptyCustomizer(),
+				HttpComponentsClientHttpRequestFactoryBuilder::createTlsSocketStrategy);
 	}
 
 	private HttpComponentsClientHttpRequestFactoryBuilder(
-			List<Consumer<HttpComponentsClientHttpRequestFactory>> customizers) {
+			List<Consumer<HttpComponentsClientHttpRequestFactory>> customizers,
+			Consumer<HttpClientBuilder> httpClientCustomizer,
+			Consumer<PoolingHttpClientConnectionManagerBuilder> connectionManagerCustomizer,
+			Consumer<SocketConfig.Builder> socketConfigCustomizer,
+			Function<SslBundle, TlsSocketStrategy> tlsSocketStrategyFactory) {
 		super(customizers);
+		this.httpClientCustomizer = httpClientCustomizer;
+		this.connectionManagerCustomizer = connectionManagerCustomizer;
+		this.socketConfigCustomizer = socketConfigCustomizer;
+		this.tlsSocketStrategyFactory = tlsSocketStrategyFactory;
 	}
 
 	@Override
 	public HttpComponentsClientHttpRequestFactoryBuilder withCustomizer(
 			Consumer<HttpComponentsClientHttpRequestFactory> customizer) {
-		return new HttpComponentsClientHttpRequestFactoryBuilder(mergedCustomizers(customizer));
+		return new HttpComponentsClientHttpRequestFactoryBuilder(mergedCustomizers(customizer),
+				this.httpClientCustomizer, this.connectionManagerCustomizer, this.socketConfigCustomizer,
+				this.tlsSocketStrategyFactory);
 	}
 
 	@Override
 	public HttpComponentsClientHttpRequestFactoryBuilder withCustomizers(
 			Collection<Consumer<HttpComponentsClientHttpRequestFactory>> customizers) {
-		return new HttpComponentsClientHttpRequestFactoryBuilder(mergedCustomizers(customizers));
+		return new HttpComponentsClientHttpRequestFactoryBuilder(mergedCustomizers(customizers),
+				this.httpClientCustomizer, this.connectionManagerCustomizer, this.socketConfigCustomizer,
+				this.tlsSocketStrategyFactory);
+	}
+
+	/**
+	 * Return a new {@link HttpComponentsClientHttpRequestFactoryBuilder} that applies
+	 * additional customization to the underlying {@link HttpClientBuilder}.
+	 * @param httpClientCustomizer the customizer to apply
+	 * @return a new {@link HttpComponentsClientHttpRequestFactoryBuilder} instance
+	 */
+	public HttpComponentsClientHttpRequestFactoryBuilder withHttpClientCustomizer(
+			Consumer<HttpClientBuilder> httpClientCustomizer) {
+		Assert.notNull(httpClientCustomizer, "'httpClientCustomizer' must not be null");
+		return new HttpComponentsClientHttpRequestFactoryBuilder(getCustomizers(),
+				this.httpClientCustomizer.andThen(httpClientCustomizer), this.connectionManagerCustomizer,
+				this.socketConfigCustomizer, this.tlsSocketStrategyFactory);
+	}
+
+	/**
+	 * Return a new {@link HttpComponentsClientHttpRequestFactoryBuilder} that applies
+	 * additional customization to the underlying
+	 * {@link PoolingHttpClientConnectionManagerBuilder}.
+	 * @param connectionManagerCustomizer the customizer to apply
+	 * @return a new {@link HttpComponentsClientHttpRequestFactoryBuilder} instance
+	 */
+	public HttpComponentsClientHttpRequestFactoryBuilder withConnectionManagerCustomizer(
+			Consumer<PoolingHttpClientConnectionManagerBuilder> connectionManagerCustomizer) {
+		Assert.notNull(connectionManagerCustomizer, "'connectionManagerCustomizer' must not be null");
+		return new HttpComponentsClientHttpRequestFactoryBuilder(getCustomizers(), this.httpClientCustomizer,
+				this.connectionManagerCustomizer.andThen(connectionManagerCustomizer), this.socketConfigCustomizer,
+				this.tlsSocketStrategyFactory);
+	}
+
+	/**
+	 * Return a new {@link HttpComponentsClientHttpRequestFactoryBuilder} that applies
+	 * additional customization to the underlying
+	 * {@link org.apache.hc.core5.http.io.SocketConfig.Builder}.
+	 * @param socketConfigCustomizer the customizer to apply
+	 * @return a new {@link HttpComponentsClientHttpRequestFactoryBuilder} instance
+	 */
+	public HttpComponentsClientHttpRequestFactoryBuilder withSocketConfigCustomizer(
+			Consumer<SocketConfig.Builder> socketConfigCustomizer) {
+		Assert.notNull(socketConfigCustomizer, "'socketConfigCustomizer' must not be null");
+		return new HttpComponentsClientHttpRequestFactoryBuilder(getCustomizers(), this.httpClientCustomizer,
+				this.connectionManagerCustomizer, this.socketConfigCustomizer.andThen(socketConfigCustomizer),
+				this.tlsSocketStrategyFactory);
+	}
+
+	/**
+	 * Return a new {@link HttpComponentsClientHttpRequestFactoryBuilder} with a
+	 * replacement {@link TlsSocketStrategy} factory.
+	 * @param tlsSocketStrategyFactory the new factory used to create a
+	 * {@link TlsSocketStrategy} for a given {@link SslBundle}
+	 * @return a new {@link HttpComponentsClientHttpRequestFactoryBuilder} instance
+	 */
+	public HttpComponentsClientHttpRequestFactoryBuilder withTlsSocketStrategyFactory(
+			Function<SslBundle, TlsSocketStrategy> tlsSocketStrategyFactory) {
+		Assert.notNull(tlsSocketStrategyFactory, "'tlsSocketStrategyFactory' must not be null");
+		return new HttpComponentsClientHttpRequestFactoryBuilder(getCustomizers(), this.httpClientCustomizer,
+				this.connectionManagerCustomizer, this.socketConfigCustomizer, tlsSocketStrategyFactory);
 	}
 
 	@Override
@@ -87,11 +169,12 @@ public final class HttpComponentsClientHttpRequestFactoryBuilder
 	}
 
 	private HttpClient createHttpClient(ClientHttpRequestFactorySettings settings) {
-		return HttpClientBuilder.create()
+		HttpClientBuilder builder = HttpClientBuilder.create()
 			.useSystemProperties()
 			.setRedirectStrategy(asRedirectStrategy(settings.redirects()))
-			.setConnectionManager(createConnectionManager(settings))
-			.build();
+			.setConnectionManager(createConnectionManager(settings));
+		this.httpClientCustomizer.accept(builder);
+		return builder.build();
 	}
 
 	private RedirectStrategy asRedirectStrategy(Redirects redirects) {
@@ -102,23 +185,31 @@ public final class HttpComponentsClientHttpRequestFactoryBuilder
 	}
 
 	private PoolingHttpClientConnectionManager createConnectionManager(ClientHttpRequestFactorySettings settings) {
-		PoolingHttpClientConnectionManagerBuilder builder = PoolingHttpClientConnectionManagerBuilder.create();
+		PoolingHttpClientConnectionManagerBuilder builder = PoolingHttpClientConnectionManagerBuilder.create()
+			.useSystemProperties();
 		PropertyMapper map = PropertyMapper.get().alwaysApplyingWhenNonNull();
-		map.from(settings::readTimeout).as(this::createSocketConfig).to(builder::setDefaultSocketConfig);
-		map.from(settings::sslBundle).as(this::createTlsSocketStrategy).to(builder::setTlsSocketStrategy);
-		return builder.useSystemProperties().build();
+		builder.setDefaultSocketConfig(createSocketConfig(settings));
+		map.from(settings::sslBundle).as(this.tlsSocketStrategyFactory).to(builder::setTlsSocketStrategy);
+		this.connectionManagerCustomizer.accept(builder);
+		return builder.build();
 	}
 
-	private DefaultClientTlsStrategy createTlsSocketStrategy(SslBundle sslBundle) {
+	private SocketConfig createSocketConfig(ClientHttpRequestFactorySettings settings) {
+		SocketConfig.Builder builder = SocketConfig.custom();
+		PropertyMapper map = PropertyMapper.get().alwaysApplyingWhenNonNull();
+		map.from(settings::readTimeout)
+			.asInt(Duration::toMillis)
+			.to((timeout) -> builder.setSoTimeout(timeout, TimeUnit.MILLISECONDS));
+		this.socketConfigCustomizer.accept(builder);
+		return builder.build();
+	}
+
+	private static TlsSocketStrategy createTlsSocketStrategy(SslBundle sslBundle) {
 		SslOptions options = sslBundle.getOptions();
 		return new DefaultClientTlsStrategy(sslBundle.createSslContext(), options.getEnabledProtocols(),
 				options.getCiphers(), null, new DefaultHostnameVerifier());
 	}
 
-	private SocketConfig createSocketConfig(Duration readTimeout) {
-		return SocketConfig.custom().setSoTimeout((int) readTimeout.toMillis(), TimeUnit.MILLISECONDS).build();
-	}
-
 	/**
 	 * {@link RedirectStrategy} that never follows redirects.
 	 */

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/http/client/JdkClientHttpRequestFactoryBuilder.java

@@ -26,6 +26,7 @@ import org.springframework.boot.context.properties.PropertyMapper;
 import org.springframework.boot.http.client.ClientHttpRequestFactorySettings.Redirects;
 import org.springframework.boot.ssl.SslBundle;
 import org.springframework.http.client.JdkClientHttpRequestFactory;
+import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 
 /**
@@ -39,23 +40,40 @@ import org.springframework.util.ClassUtils;
 public class JdkClientHttpRequestFactoryBuilder
 		extends AbstractClientHttpRequestFactoryBuilder<JdkClientHttpRequestFactory> {
 
+	private final Consumer<HttpClient.Builder> httpClientCustomizer;
+
 	JdkClientHttpRequestFactoryBuilder() {
-		this(null);
+		this(null, emptyCustomizer());
 	}
 
-	private JdkClientHttpRequestFactoryBuilder(List<Consumer<JdkClientHttpRequestFactory>> customizers) {
+	private JdkClientHttpRequestFactoryBuilder(List<Consumer<JdkClientHttpRequestFactory>> customizers,
+			Consumer<HttpClient.Builder> httpClientCustomizer) {
 		super(customizers);
+		this.httpClientCustomizer = httpClientCustomizer;
 	}
 
 	@Override
 	public JdkClientHttpRequestFactoryBuilder withCustomizer(Consumer<JdkClientHttpRequestFactory> customizer) {
-		return new JdkClientHttpRequestFactoryBuilder(mergedCustomizers(customizer));
+		return new JdkClientHttpRequestFactoryBuilder(mergedCustomizers(customizer), this.httpClientCustomizer);
 	}
 
 	@Override
 	public JdkClientHttpRequestFactoryBuilder withCustomizers(
 			Collection<Consumer<JdkClientHttpRequestFactory>> customizers) {
-		return new JdkClientHttpRequestFactoryBuilder(mergedCustomizers(customizers));
+		return new JdkClientHttpRequestFactoryBuilder(mergedCustomizers(customizers), this.httpClientCustomizer);
+	}
+
+	/**
+	 * Return a new {@link JdkClientHttpRequestFactoryBuilder} that applies additional
+	 * customization to the underlying {@link java.net.http.HttpClient.Builder}.
+	 * @param httpClientCustomizer the customizer to apply
+	 * @return a new {@link JdkClientHttpRequestFactoryBuilder} instance
+	 */
+	public JdkClientHttpRequestFactoryBuilder withHttpClientCustomizer(
+			Consumer<HttpClient.Builder> httpClientCustomizer) {
+		Assert.notNull(httpClientCustomizer, "'httpClientCustomizer' must not be null");
+		return new JdkClientHttpRequestFactoryBuilder(getCustomizers(),
+				this.httpClientCustomizer.andThen(httpClientCustomizer));
 	}
 
 	@Override
@@ -68,12 +86,13 @@ public class JdkClientHttpRequestFactoryBuilder
 	}
 
 	private HttpClient createHttpClient(ClientHttpRequestFactorySettings settings) {
-		HttpClient.Builder httpClientBuilder = HttpClient.newBuilder();
+		HttpClient.Builder builder = HttpClient.newBuilder();
 		PropertyMapper map = PropertyMapper.get().alwaysApplyingWhenNonNull();
-		map.from(settings::connectTimeout).to(httpClientBuilder::connectTimeout);
-		map.from(settings::sslBundle).as(SslBundle::createSslContext).to(httpClientBuilder::sslContext);
-		map.from(settings::redirects).as(this::asHttpClientRedirect).to(httpClientBuilder::followRedirects);
-		return httpClientBuilder.build();
+		map.from(settings::connectTimeout).to(builder::connectTimeout);
+		map.from(settings::sslBundle).as(SslBundle::createSslContext).to(builder::sslContext);
+		map.from(settings::redirects).as(this::asHttpClientRedirect).to(builder::followRedirects);
+		this.httpClientCustomizer.accept(builder);
+		return builder.build();
 	}
 
 	private Redirect asHttpClientRedirect(Redirects redirects) {

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/http/client/JettyClientHttpRequestFactoryBuilder.java

@@ -34,6 +34,7 @@ import org.springframework.boot.context.properties.PropertyMapper;
 import org.springframework.boot.http.client.ClientHttpRequestFactorySettings.Redirects;
 import org.springframework.boot.ssl.SslBundle;
 import org.springframework.http.client.JettyClientHttpRequestFactory;
+import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 
 /**
@@ -47,23 +48,77 @@ import org.springframework.util.ClassUtils;
 public final class JettyClientHttpRequestFactoryBuilder
 		extends AbstractClientHttpRequestFactoryBuilder<JettyClientHttpRequestFactory> {
 
+	private final Consumer<HttpClient> httpClientCustomizer;
+
+	private final Consumer<HttpClientTransport> httpClientTransportCustomizer;
+
+	private final Consumer<ClientConnector> clientConnectorCustomizerCustomizer;
+
 	JettyClientHttpRequestFactoryBuilder() {
-		this(null);
+		this(null, emptyCustomizer(), emptyCustomizer(), emptyCustomizer());
 	}
 
-	private JettyClientHttpRequestFactoryBuilder(List<Consumer<JettyClientHttpRequestFactory>> customizers) {
+	private JettyClientHttpRequestFactoryBuilder(List<Consumer<JettyClientHttpRequestFactory>> customizers,
+			Consumer<HttpClient> httpClientCustomizer, Consumer<HttpClientTransport> httpClientTransportCustomizer,
+			Consumer<ClientConnector> clientConnectorCustomizerCustomizer) {
 		super(customizers);
+		this.httpClientCustomizer = httpClientCustomizer;
+		this.httpClientTransportCustomizer = httpClientTransportCustomizer;
+		this.clientConnectorCustomizerCustomizer = clientConnectorCustomizerCustomizer;
 	}
 
 	@Override
 	public JettyClientHttpRequestFactoryBuilder withCustomizer(Consumer<JettyClientHttpRequestFactory> customizer) {
-		return new JettyClientHttpRequestFactoryBuilder(mergedCustomizers(customizer));
+		return new JettyClientHttpRequestFactoryBuilder(mergedCustomizers(customizer), this.httpClientCustomizer,
+				this.httpClientTransportCustomizer, this.clientConnectorCustomizerCustomizer);
 	}
 
 	@Override
 	public JettyClientHttpRequestFactoryBuilder withCustomizers(
 			Collection<Consumer<JettyClientHttpRequestFactory>> customizers) {
-		return new JettyClientHttpRequestFactoryBuilder(mergedCustomizers(customizers));
+		return new JettyClientHttpRequestFactoryBuilder(mergedCustomizers(customizers), this.httpClientCustomizer,
+				this.httpClientTransportCustomizer, this.clientConnectorCustomizerCustomizer);
+	}
+
+	/**
+	 * Return a new {@link JettyClientHttpRequestFactoryBuilder} that applies additional
+	 * customization to the underlying {@link HttpClient}.
+	 * @param httpClientCustomizer the customizer to apply
+	 * @return a new {@link JettyClientHttpRequestFactoryBuilder} instance
+	 */
+	public JettyClientHttpRequestFactoryBuilder withHttpClientCustomizer(Consumer<HttpClient> httpClientCustomizer) {
+		Assert.notNull(httpClientCustomizer, "'httpClientCustomizer' must not be null");
+		return new JettyClientHttpRequestFactoryBuilder(getCustomizers(),
+				this.httpClientCustomizer.andThen(httpClientCustomizer), this.httpClientTransportCustomizer,
+				this.clientConnectorCustomizerCustomizer);
+	}
+
+	/**
+	 * Return a new {@link JettyClientHttpRequestFactoryBuilder} that applies additional
+	 * customization to the underlying {@link HttpClientTransport}.
+	 * @param httpClientTransportCustomizer the customizer to apply
+	 * @return a new {@link JettyClientHttpRequestFactoryBuilder} instance
+	 */
+	public JettyClientHttpRequestFactoryBuilder withHttpClientTransportCustomizer(
+			Consumer<HttpClientTransport> httpClientTransportCustomizer) {
+		Assert.notNull(httpClientTransportCustomizer, "'httpClientTransportCustomizer' must not be null");
+		return new JettyClientHttpRequestFactoryBuilder(getCustomizers(), this.httpClientCustomizer,
+				this.httpClientTransportCustomizer.andThen(httpClientTransportCustomizer),
+				this.clientConnectorCustomizerCustomizer);
+	}
+
+	/**
+	 * Return a new {@link JettyClientHttpRequestFactoryBuilder} that applies additional
+	 * customization to the underlying {@link ClientConnector}.
+	 * @param clientConnectorCustomizerCustomizer the customizer to apply
+	 * @return a new {@link JettyClientHttpRequestFactoryBuilder} instance
+	 */
+	public JettyClientHttpRequestFactoryBuilder withClientConnectorCustomizerCustomizer(
+			Consumer<ClientConnector> clientConnectorCustomizerCustomizer) {
+		Assert.notNull(clientConnectorCustomizerCustomizer, "'clientConnectorCustomizerCustomizer' must not be null");
+		return new JettyClientHttpRequestFactoryBuilder(getCustomizers(), this.httpClientCustomizer,
+				this.httpClientTransportCustomizer,
+				this.clientConnectorCustomizerCustomizer.andThen(clientConnectorCustomizerCustomizer));
 	}
 
 	@Override
@@ -77,27 +132,34 @@ public final class JettyClientHttpRequestFactoryBuilder
 
 	private JettyClientHttpRequestFactory createRequestFactory(ClientHttpRequestFactorySettings settings) {
 		HttpClientTransport transport = createTransport(settings);
+		this.httpClientTransportCustomizer.accept(transport);
 		HttpClient httpClient = new HttpClient(transport);
 		PropertyMapper map = PropertyMapper.get().alwaysApplyingWhenNonNull();
 		map.from(settings::redirects).as(this::followRedirects).to(httpClient::setFollowRedirects);
+		this.httpClientCustomizer.accept(httpClient);
 		return new JettyClientHttpRequestFactory(httpClient);
 	}
 
 	private HttpClientTransport createTransport(ClientHttpRequestFactorySettings settings) {
-		if (settings.sslBundle() == null) {
-			return new HttpClientTransportOverHTTP();
-		}
 		ClientConnector connector = createClientConnector(settings.sslBundle());
-		return new HttpClientTransportDynamic(connector);
+		return (connector.getSslContextFactory() != null) ? new HttpClientTransportDynamic(connector)
+				: new HttpClientTransportOverHTTP(connector);
 	}
 
 	private ClientConnector createClientConnector(SslBundle sslBundle) {
+		ClientConnector connector = new ClientConnector();
+		if (sslBundle != null) {
+			connector.setSslContextFactory(createSslContextFactory(sslBundle));
+		}
+		this.clientConnectorCustomizerCustomizer.accept(connector);
+		return connector;
+	}
+
+	private SslContextFactory.Client createSslContextFactory(SslBundle sslBundle) {
 		SSLContext sslContext = sslBundle.createSslContext();
 		SslContextFactory.Client sslContextFactory = new SslContextFactory.Client();
 		sslContextFactory.setSslContext(sslContext);
-		ClientConnector connector = new ClientConnector();
-		connector.setSslContextFactory(sslContextFactory);
-		return connector;
+		return sslContextFactory;
 	}
 
 	private boolean followRedirects(Redirects redirects) {

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/http/client/ReactorClientHttpRequestFactoryBuilder.java

@@ -20,6 +20,7 @@ import java.time.Duration;
 import java.util.Collection;
 import java.util.List;
 import java.util.function.Consumer;
+import java.util.function.UnaryOperator;
 
 import javax.net.ssl.SSLException;
 
@@ -33,6 +34,7 @@ import org.springframework.boot.ssl.SslBundle;
 import org.springframework.boot.ssl.SslManagerBundle;
 import org.springframework.boot.ssl.SslOptions;
 import org.springframework.http.client.ReactorClientHttpRequestFactory;
+import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.function.ThrowingConsumer;
 
@@ -47,23 +49,40 @@ import org.springframework.util.function.ThrowingConsumer;
 public final class ReactorClientHttpRequestFactoryBuilder
 		extends AbstractClientHttpRequestFactoryBuilder<ReactorClientHttpRequestFactory> {
 
+	private final UnaryOperator<HttpClient> httpClientCustomizer;
+
 	ReactorClientHttpRequestFactoryBuilder() {
-		this(null);
+		this(null, UnaryOperator.identity());
 	}
 
-	private ReactorClientHttpRequestFactoryBuilder(List<Consumer<ReactorClientHttpRequestFactory>> customizers) {
+	private ReactorClientHttpRequestFactoryBuilder(List<Consumer<ReactorClientHttpRequestFactory>> customizers,
+			UnaryOperator<HttpClient> httpClientCustomizer) {
 		super(customizers);
+		this.httpClientCustomizer = httpClientCustomizer;
 	}
 
 	@Override
 	public ReactorClientHttpRequestFactoryBuilder withCustomizer(Consumer<ReactorClientHttpRequestFactory> customizer) {
-		return new ReactorClientHttpRequestFactoryBuilder(mergedCustomizers(customizer));
+		return new ReactorClientHttpRequestFactoryBuilder(mergedCustomizers(customizer), this.httpClientCustomizer);
 	}
 
 	@Override
 	public ReactorClientHttpRequestFactoryBuilder withCustomizers(
 			Collection<Consumer<ReactorClientHttpRequestFactory>> customizers) {
-		return new ReactorClientHttpRequestFactoryBuilder(mergedCustomizers(customizers));
+		return new ReactorClientHttpRequestFactoryBuilder(mergedCustomizers(customizers), this.httpClientCustomizer);
+	}
+
+	/**
+	 * Return a new {@link ReactorClientHttpRequestFactoryBuilder} that applies additional
+	 * customization to the underlying {@link HttpClient}.
+	 * @param httpClientCustomizer the customizer to apply
+	 * @return a new {@link ReactorClientHttpRequestFactoryBuilder} instance
+	 */
+	public ReactorClientHttpRequestFactoryBuilder withHttpClientCustomizer(
+			UnaryOperator<HttpClient> httpClientCustomizer) {
+		Assert.notNull(httpClientCustomizer, "'httpClientCustomizer' must not be null");
+		return new ReactorClientHttpRequestFactoryBuilder(getCustomizers(),
+				(t) -> httpClientCustomizer.apply(this.httpClientCustomizer.apply(t)));
 	}
 
 	@Override
@@ -82,6 +101,7 @@ public final class ReactorClientHttpRequestFactoryBuilder
 		if (settings.sslBundle() != null) {
 			httpClient = httpClient.secure((ThrowingConsumer.of((spec) -> configureSsl(spec, settings.sslBundle()))));
 		}
+		httpClient = this.httpClientCustomizer.apply(httpClient);
 		return new ReactorClientHttpRequestFactory(httpClient);
 	}
 

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/http/client/HttpComponentsClientHttpRequestFactoryBuilderTests.java

@@ -16,14 +16,26 @@
 
 package org.springframework.boot.http.client;
 
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Function;
+
 import org.apache.hc.client5.http.HttpRoute;
 import org.apache.hc.client5.http.classic.HttpClient;
+import org.apache.hc.client5.http.impl.classic.HttpClientBuilder;
+import org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManagerBuilder;
+import org.apache.hc.client5.http.ssl.TlsSocketStrategy;
 import org.apache.hc.core5.function.Resolver;
 import org.apache.hc.core5.http.io.SocketConfig;
+import org.apache.hc.core5.http.io.SocketConfig.Builder;
+import org.junit.jupiter.api.Test;
 
+import org.springframework.boot.ssl.SslBundle;
 import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
 import org.springframework.test.util.ReflectionTestUtils;
 
+import static org.assertj.core.api.Assertions.assertThat;
+
 /**
  * Tests for {@link HttpComponentsClientHttpRequestFactoryBuilder}.
  *
@@ -37,6 +49,38 @@ class HttpComponentsClientHttpRequestFactoryBuilderTests
 		super(HttpComponentsClientHttpRequestFactory.class, ClientHttpRequestFactoryBuilder.httpComponents());
 	}
 
+	@Test
+	void withCustomizers() {
+		TestCustomizer<HttpClientBuilder> httpClientCustomizer1 = new TestCustomizer<>();
+		TestCustomizer<HttpClientBuilder> httpClientCustomizer2 = new TestCustomizer<>();
+		TestCustomizer<PoolingHttpClientConnectionManagerBuilder> connectionManagerCustomizer = new TestCustomizer<>();
+		TestCustomizer<Builder> socketConfigCustomizer = new TestCustomizer<>();
+		ClientHttpRequestFactoryBuilder.httpComponents()
+			.withHttpClientCustomizer(httpClientCustomizer1)
+			.withHttpClientCustomizer(httpClientCustomizer2)
+			.withConnectionManagerCustomizer(connectionManagerCustomizer)
+			.withSocketConfigCustomizer(socketConfigCustomizer)
+			.build();
+		httpClientCustomizer1.assertCalled();
+		httpClientCustomizer2.assertCalled();
+		connectionManagerCustomizer.assertCalled();
+		socketConfigCustomizer.assertCalled();
+	}
+
+	@Test
+	void withTlsSocketStrategyFactory() {
+		ClientHttpRequestFactorySettings settings = ClientHttpRequestFactorySettings.ofSslBundle(sslBundle());
+		List<SslBundle> bundles = new ArrayList<>();
+		Function<SslBundle, TlsSocketStrategy> tlsSocketStrategyFactory = (bundle) -> {
+			bundles.add(bundle);
+			return (socket, target, port, attachment, context) -> null;
+		};
+		ClientHttpRequestFactoryBuilder.httpComponents()
+			.withTlsSocketStrategyFactory(tlsSocketStrategyFactory)
+			.build(settings);
+		assertThat(bundles).contains(settings.sslBundle());
+	}
+
 	@Override
 	protected long connectTimeout(HttpComponentsClientHttpRequestFactory requestFactory) {
 		return (long) ReflectionTestUtils.getField(requestFactory, "connectTimeout");

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/http/client/JdkClientHttpRequestFactoryBuilderTests.java

@@ -19,6 +19,8 @@ package org.springframework.boot.http.client;
 import java.net.http.HttpClient;
 import java.time.Duration;
 
+import org.junit.jupiter.api.Test;
+
 import org.springframework.http.client.JdkClientHttpRequestFactory;
 import org.springframework.test.util.ReflectionTestUtils;
 
@@ -34,6 +36,18 @@ class JdkClientHttpRequestFactoryBuilderTests
 		super(JdkClientHttpRequestFactory.class, ClientHttpRequestFactoryBuilder.jdk());
 	}
 
+	@Test
+	void withCustomizers() {
+		TestCustomizer<HttpClient.Builder> httpClientCustomizer1 = new TestCustomizer<>();
+		TestCustomizer<HttpClient.Builder> httpClientCustomizer2 = new TestCustomizer<>();
+		ClientHttpRequestFactoryBuilder.jdk()
+			.withHttpClientCustomizer(httpClientCustomizer1)
+			.withHttpClientCustomizer(httpClientCustomizer2)
+			.build();
+		httpClientCustomizer1.assertCalled();
+		httpClientCustomizer2.assertCalled();
+	}
+
 	@Override
 	protected long connectTimeout(JdkClientHttpRequestFactory requestFactory) {
 		HttpClient httpClient = (HttpClient) ReflectionTestUtils.getField(requestFactory, "httpClient");

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/http/client/JettyClientHttpRequestFactoryBuilderTests.java

@@ -17,6 +17,9 @@
 package org.springframework.boot.http.client;
 
 import org.eclipse.jetty.client.HttpClient;
+import org.eclipse.jetty.client.HttpClientTransport;
+import org.eclipse.jetty.io.ClientConnector;
+import org.junit.jupiter.api.Test;
 
 import org.springframework.http.client.JettyClientHttpRequestFactory;
 import org.springframework.test.util.ReflectionTestUtils;
@@ -33,6 +36,24 @@ class JettyClientHttpRequestFactoryBuilderTests
 		super(JettyClientHttpRequestFactory.class, ClientHttpRequestFactoryBuilder.jetty());
 	}
 
+	@Test
+	void withCustomizers() {
+		TestCustomizer<HttpClient> httpClientCustomizer1 = new TestCustomizer<>();
+		TestCustomizer<HttpClient> httpClientCustomizer2 = new TestCustomizer<>();
+		TestCustomizer<HttpClientTransport> httpClientTransportCustomizer = new TestCustomizer<>();
+		TestCustomizer<ClientConnector> clientConnectorCustomizerCustomizer = new TestCustomizer<>();
+		ClientHttpRequestFactoryBuilder.jetty()
+			.withHttpClientCustomizer(httpClientCustomizer1)
+			.withHttpClientCustomizer(httpClientCustomizer2)
+			.withHttpClientTransportCustomizer(httpClientTransportCustomizer)
+			.withClientConnectorCustomizerCustomizer(clientConnectorCustomizerCustomizer)
+			.build();
+		httpClientCustomizer1.assertCalled();
+		httpClientCustomizer2.assertCalled();
+		httpClientTransportCustomizer.assertCalled();
+		clientConnectorCustomizerCustomizer.assertCalled();
+	}
+
 	@Override
 	protected long connectTimeout(JettyClientHttpRequestFactory requestFactory) {
 		return ((HttpClient) ReflectionTestUtils.getField(requestFactory, "httpClient")).getConnectTimeout();

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/http/client/ReactorClientHttpRequestFactoryBuilderTests.java

@@ -17,13 +17,19 @@
 package org.springframework.boot.http.client;
 
 import java.time.Duration;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.UnaryOperator;
 
 import io.netty.channel.ChannelOption;
+import org.junit.jupiter.api.Test;
 import reactor.netty.http.client.HttpClient;
 
 import org.springframework.http.client.ReactorClientHttpRequestFactory;
 import org.springframework.test.util.ReflectionTestUtils;
 
+import static org.assertj.core.api.Assertions.assertThat;
+
 /**
  * Tests for {@link ReactorClientHttpRequestFactoryBuilder}.
  *
@@ -37,6 +43,24 @@ class ReactorClientHttpRequestFactoryBuilderTests
 		super(ReactorClientHttpRequestFactory.class, ClientHttpRequestFactoryBuilder.reactor());
 	}
 
+	@Test
+	void withCustomizers() {
+		List<HttpClient> httpClients = new ArrayList<>();
+		UnaryOperator<HttpClient> httpClientCustomizer1 = (httpClient) -> {
+			httpClients.add(httpClient);
+			return httpClient;
+		};
+		UnaryOperator<HttpClient> httpClientCustomizer2 = (httpClient) -> {
+			httpClients.add(httpClient);
+			return httpClient;
+		};
+		ClientHttpRequestFactoryBuilder.reactor()
+			.withHttpClientCustomizer(httpClientCustomizer1)
+			.withHttpClientCustomizer(httpClientCustomizer2)
+			.build();
+		assertThat(httpClients).hasSize(2);
+	}
+
 	@Override
 	protected long connectTimeout(ReactorClientHttpRequestFactory requestFactory) {
 		return (int) ((HttpClient) ReflectionTestUtils.getField(requestFactory, "httpClient")).configuration()

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/http/client/TestCustomizer.java

@@ -0,0 +1,42 @@
+/*
+ * 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.http.client;
+
+import java.util.function.Consumer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Test customizer that can assert that it has been called.
+ *
+ * @param <T> type being customized
+ * @author Phillip Webb
+ */
+class TestCustomizer<T> implements Consumer<T> {
+
+	private boolean called;
+
+	@Override
+	public void accept(T t) {
+		this.called = true;
+	}
+
+	void assertCalled() {
+		assertThat(this.called).isTrue();
+	}
+
+}