Add HttpClientBuilderCustomizer interface

In addition to leveraging existing Spring Cloud settings, provide the ability for a user to customize settings.

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/clientconfig/HttpClient5FeignConfiguration.java

@@ -31,6 +31,7 @@
 import org.apache.commons.logging.LogFactory;
 import org.apache.hc.client5.http.config.RequestConfig;
 import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
+import org.apache.hc.client5.http.impl.classic.HttpClientBuilder;
 import org.apache.hc.client5.http.impl.classic.HttpClients;
 import org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManagerBuilder;
 import org.apache.hc.client5.http.io.HttpClientConnectionManager;
@@ -46,6 +47,7 @@
 import org.apache.hc.core5.util.TimeValue;
 import org.apache.hc.core5.util.Timeout;
 
+import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.cloud.openfeign.support.FeignHttpClientProperties;
 import org.springframework.context.annotation.Bean;
@@ -85,18 +87,23 @@ public HttpClientConnectionManager hc5ConnectionManager(FeignHttpClientPropertie
 
 	@Bean
 	public CloseableHttpClient httpClient5(HttpClientConnectionManager connectionManager,
-			FeignHttpClientProperties httpClientProperties) {
-		httpClient5 = HttpClients.custom().disableCookieManagement().useSystemProperties()
-				.setConnectionManager(connectionManager).evictExpiredConnections()
-				.setDefaultRequestConfig(RequestConfig.custom()
-						.setConnectTimeout(
-								Timeout.of(httpClientProperties.getConnectionTimeout(), TimeUnit.MILLISECONDS))
-						.setRedirectsEnabled(httpClientProperties.isFollowRedirects())
-						.setConnectionRequestTimeout(
-								Timeout.of(httpClientProperties.getHc5().getConnectionRequestTimeout(),
-										httpClientProperties.getHc5().getConnectionRequestTimeoutUnit()))
-						.build())
-				.build();
+			FeignHttpClientProperties httpClientProperties,
+			ObjectProvider<List<HttpClientBuilderCustomizer>> customizerProvider) {
+		HttpClientBuilder httpClientBuilder = HttpClients.custom().disableCookieManagement().useSystemProperties()
+			.setConnectionManager(connectionManager).evictExpiredConnections()
+			.setDefaultRequestConfig(RequestConfig.custom()
+				.setConnectTimeout(
+					Timeout.of(httpClientProperties.getConnectionTimeout(), TimeUnit.MILLISECONDS))
+				.setRedirectsEnabled(httpClientProperties.isFollowRedirects())
+				.setConnectionRequestTimeout(
+					Timeout.of(httpClientProperties.getHc5().getConnectionRequestTimeout(),
+						httpClientProperties.getHc5().getConnectionRequestTimeoutUnit()))
+				.build());
+
+		customizerProvider.getIfAvailable(List::of)
+			.forEach(c -> c.customize(httpClientBuilder));
+
+		httpClient5 = httpClientBuilder.build();
 		return httpClient5;
 	}
 
@@ -146,4 +153,9 @@ public X509Certificate[] getAcceptedIssuers() {
 
 	}
 
+	public interface HttpClientBuilderCustomizer {
+
+		void customize(HttpClientBuilder builder);
+
+	}
 }