Allow SSL configuration with the Elasticsearch CA fingerprint.

src/main/asciidoc/reference/elasticsearch-clients.adoc

@@ -240,7 +240,7 @@ ClientConfiguration clientConfiguration = ClientConfiguration.builder()
 
 <.> Define default headers, if they need to be customized
 <.> Use the builder to provide cluster addresses, set default `HttpHeaders` or enable SSL.
-<.> Optionally enable SSL.
+<.> Optionally enable SSL. There exist overloads of this function that can take a `SSLContext` or as an alternative the fingerprint of the certificate as it is output by Elasticsearch 8 on startup.
 <.> Optionally set a proxy.
 <.> Optionally set a path prefix, mostly used when different clusters a behind some reverse proxy.
 <.> Set the connection timeout.

src/main/asciidoc/reference/elasticsearch-new.adoc

@@ -5,6 +5,7 @@
 == New in Spring Data Elasticsearch 5.1
 
 * Upgrade to Elasticsearch 8.7.0
+* Allow specification of the TLS certificate when connecting to an Elasticsearch 8 cluster 
 
 [[new-features.5-0-0]]
 == New in Spring Data Elasticsearch 5.0

src/main/java/org/springframework/data/elasticsearch/client/ClientConfiguration.java

@@ -20,15 +20,13 @@
 import java.time.Duration;
 import java.util.List;
 import java.util.Optional;
-import java.util.function.Function;
 import java.util.function.Supplier;
 
 import javax.net.ssl.HostnameVerifier;
 import javax.net.ssl.SSLContext;
 
 import org.springframework.data.elasticsearch.support.HttpHeaders;
 import org.springframework.lang.Nullable;
-import org.springframework.web.reactive.function.client.WebClient;
 
 /**
  * Configuration interface exposing common client configuration properties for Elasticsearch clients.
@@ -122,6 +120,12 @@ static ClientConfiguration create(InetSocketAddress socketAddress) {
 	 */
 	Optional<SSLContext> getSslContext();
 
+	/**
+	 * @return the optional SHA-256 fingerprint of the self-signed http_ca.crt certificate output by Elasticsearch at
+	 *         startup time.
+	 */
+	Optional<String> getCaFingerprint();
+
 	/**
 	 * Returns the {@link HostnameVerifier} to use. Can be {@link Optional#empty()} if not configured.
 	 *
@@ -250,6 +254,15 @@ interface MaybeSecureClientConfigurationBuilder extends TerminalClientConfigurat
 		 * @return the {@link TerminalClientConfigurationBuilder}.
 		 */
 		TerminalClientConfigurationBuilder usingSsl(SSLContext sslContext, HostnameVerifier hostnameVerifier);
+
+		/**
+		 * Connect via https using a SSLContext that is build from the given certificate fingerprint.
+		 *
+		 * @param caFingerprint the SHA-256 fingerprint of the self-signed http_ca.crt certificate output by Elasticsearch
+		 *          at startup time.
+		 * @return the {@link TerminalClientConfigurationBuilder}.
+		 */
+		TerminalClientConfigurationBuilder usingSsl(String caFingerprint);
 	}
 
 	/**

src/main/java/org/springframework/data/elasticsearch/client/ClientConfigurationBuilder.java

@@ -20,7 +20,6 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
-import java.util.function.Function;
 import java.util.function.Supplier;
 
 import javax.net.ssl.HostnameVerifier;
@@ -33,7 +32,6 @@
 import org.springframework.data.elasticsearch.support.HttpHeaders;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
-import org.springframework.web.reactive.function.client.WebClient;
 
 /**
  * Default builder implementation for {@link ClientConfiguration}.
@@ -51,14 +49,15 @@ class ClientConfigurationBuilder
 	private final List<InetSocketAddress> hosts = new ArrayList<>();
 	private HttpHeaders headers = new HttpHeaders();
 	private boolean useSsl;
-	private @Nullable SSLContext sslContext;
-	private @Nullable HostnameVerifier hostnameVerifier;
+	@Nullable private SSLContext sslContext;
+	@Nullable private String caFingerprint;
+	@Nullable private HostnameVerifier hostnameVerifier;
 	private Duration connectTimeout = Duration.ofSeconds(10);
 	private Duration soTimeout = Duration.ofSeconds(5);
-	private @Nullable String username;
-	private @Nullable String password;
-	private @Nullable String pathPrefix;
-	private @Nullable String proxy;
+	@Nullable private String username;
+	@Nullable private String password;
+	@Nullable private String pathPrefix;
+	@Nullable private String proxy;
 	private Supplier<HttpHeaders> headersSupplier = HttpHeaders::new;
 	@Deprecated private final HttpClientConfigCallback httpClientConfigurer = httpClientBuilder -> httpClientBuilder;
 	private final List<ClientConfiguration.ClientConfigurationCallback<?>> clientConfigurers = new ArrayList<>();
@@ -138,10 +137,20 @@ public TerminalClientConfigurationBuilder usingSsl(SSLContext sslContext, Hostna
 		return this;
 	}
 
+	@Override
+	public TerminalClientConfigurationBuilder usingSsl(String caFingerprint) {
+
+		Assert.notNull(caFingerprint, "caFingerprint must not be null");
+
+		this.useSsl = true;
+		this.caFingerprint = caFingerprint;
+		return this;
+	}
+
 	/*
-	 * (non-Javadoc)
-	 * @see org.springframework.data.elasticsearch.client.ClientConfiguration.TerminalClientConfigurationBuilder#withDefaultHeaders(org.springframework.http.HttpHeaders)
-	 */
+	* (non-Javadoc)
+	* @see org.springframework.data.elasticsearch.client.ClientConfiguration.TerminalClientConfigurationBuilder#withDefaultHeaders(org.springframework.http.HttpHeaders)
+	*/
 	@Override
 	public TerminalClientConfigurationBuilder withDefaultHeaders(HttpHeaders defaultHeaders) {
 
@@ -228,8 +237,12 @@ public ClientConfiguration build() {
 			headers.setBasicAuth(username, password);
 		}
 
-		return new DefaultClientConfiguration(hosts, headers, useSsl, sslContext, soTimeout, connectTimeout, pathPrefix,
-				hostnameVerifier, proxy, httpClientConfigurer, clientConfigurers, headersSupplier);
+		if (sslContext != null && caFingerprint != null) {
+			throw new IllegalArgumentException("Either SSLContext or caFingerprint must be set, but not both");
+		}
+
+		return new DefaultClientConfiguration(hosts, headers, useSsl, sslContext, caFingerprint, soTimeout, connectTimeout,
+				pathPrefix, hostnameVerifier, proxy, httpClientConfigurer, clientConfigurers, headersSupplier);
 	}
 
 	private static InetSocketAddress parse(String hostAndPort) {

src/main/java/org/springframework/data/elasticsearch/client/DefaultClientConfiguration.java

@@ -42,26 +42,28 @@ class DefaultClientConfiguration implements ClientConfiguration {
 	private final List<InetSocketAddress> hosts;
 	private final HttpHeaders headers;
 	private final boolean useSsl;
-	private final @Nullable SSLContext sslContext;
+	@Nullable private final SSLContext sslContext;
+	@Nullable private final String caFingerprint;
 	private final Duration soTimeout;
 	private final Duration connectTimeout;
-	private final @Nullable String pathPrefix;
-	private final @Nullable HostnameVerifier hostnameVerifier;
-	private final @Nullable String proxy;
+	@Nullable private final String pathPrefix;
+	@Nullable private final HostnameVerifier hostnameVerifier;
+	@Nullable private final String proxy;
 	private final HttpClientConfigCallback httpClientConfigurer;
 	private final Supplier<HttpHeaders> headersSupplier;
 	private final List<ClientConfigurationCallback<?>> clientConfigurers;
 
 	DefaultClientConfiguration(List<InetSocketAddress> hosts, HttpHeaders headers, boolean useSsl,
-			@Nullable SSLContext sslContext, Duration soTimeout, Duration connectTimeout, @Nullable String pathPrefix,
-			@Nullable HostnameVerifier hostnameVerifier, @Nullable String proxy,
+			@Nullable SSLContext sslContext, @Nullable String caFingerprint, Duration soTimeout, Duration connectTimeout,
+			@Nullable String pathPrefix, @Nullable HostnameVerifier hostnameVerifier, @Nullable String proxy,
 			HttpClientConfigCallback httpClientConfigurer, List<ClientConfigurationCallback<?>> clientConfigurers,
 			Supplier<HttpHeaders> headersSupplier) {
 
 		this.hosts = List.copyOf(hosts);
 		this.headers = headers;
 		this.useSsl = useSsl;
 		this.sslContext = sslContext;
+		this.caFingerprint = caFingerprint;
 		this.soTimeout = soTimeout;
 		this.connectTimeout = connectTimeout;
 		this.pathPrefix = pathPrefix;
@@ -92,6 +94,11 @@ public Optional<SSLContext> getSslContext() {
 		return Optional.ofNullable(this.sslContext);
 	}
 
+	@Override
+	public Optional<String> getCaFingerprint() {
+		return Optional.ofNullable(this.caFingerprint);
+	}
+
 	@Override
 	public Optional<HostnameVerifier> getHostNameVerifier() {
 		return Optional.ofNullable(this.hostnameVerifier);

src/main/java/org/springframework/data/elasticsearch/client/elc/ElasticsearchClients.java

@@ -19,6 +19,7 @@
 import co.elastic.clients.json.jackson.JacksonJsonpMapper;
 import co.elastic.clients.transport.ElasticsearchTransport;
 import co.elastic.clients.transport.TransportOptions;
+import co.elastic.clients.transport.TransportUtils;
 import co.elastic.clients.transport.Version;
 import co.elastic.clients.transport.rest_client.RestClientOptions;
 import co.elastic.clients.transport.rest_client.RestClientTransport;
@@ -34,13 +35,7 @@
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
-import org.apache.http.HttpEntity;
-import org.apache.http.HttpEntityEnclosingRequest;
-import org.apache.http.HttpHost;
-import org.apache.http.HttpRequest;
-import org.apache.http.HttpRequestInterceptor;
-import org.apache.http.HttpResponse;
-import org.apache.http.HttpResponseInterceptor;
+import org.apache.http.*;
 import org.apache.http.client.config.RequestConfig;
 import org.apache.http.entity.ByteArrayEntity;
 import org.apache.http.entity.ContentType;
@@ -197,6 +192,10 @@ private static RestClientBuilder getRestClientBuilder(ClientConfiguration client
 		}
 
 		builder.setHttpClientConfigCallback(clientBuilder -> {
+			if (clientConfiguration.getCaFingerprint().isPresent()) {
+				clientBuilder
+						.setSSLContext(TransportUtils.sslContextFromCaFingerprint(clientConfiguration.getCaFingerprint().get()));
+			}
 			clientConfiguration.getSslContext().ifPresent(clientBuilder::setSSLContext);
 			clientConfiguration.getHostNameVerifier().ifPresent(clientBuilder::setSSLHostnameVerifier);
 			clientBuilder.addInterceptorLast(new CustomHeaderInjector(clientConfiguration.getHeadersSupplier()));