Add support for client certificate authentication

couchbase-analytics-java-client/src/main/java/com/couchbase/analytics/client/java/Cluster.java

@@ -39,10 +39,12 @@ public class Cluster implements Queryable, Closeable {
     .pathComponentTransformer(Cluster::lowerSnakeCaseToLowerCamelCase)
     .build();
 
-  final QueryExecutor queryExecutor;
+  volatile QueryExecutor queryExecutor;
+  private volatile Credential credential;
 
   private final String connectionString;
   private final ClusterOptions.Unmodifiable options;
+  private final HttpUrl url;
 
   private static HttpUrl parseAnalyticsUrl(String s) {
     HttpUrl url = HttpUrl.get(s);
@@ -71,19 +73,30 @@ private static HttpUrl parseAnalyticsUrl(String s) {
     return builder.build();
   }
 
-  private Cluster(String connectionString, Credential credential, ClusterOptions.Unmodifiable options) {
+  private Cluster(String connectionString, Credential initalCredential, ClusterOptions.Unmodifiable options) {
     this.connectionString = requireNonNull(connectionString);
     this.options = requireNonNull(options);
+    this.credential = requireNonNull(initalCredential);
+    this.url = parseAnalyticsUrl(connectionString);
+    this.queryExecutor = newQueryExecutor(this.options, this.url, this.credential);
+    warnIfConfigurationIsInsecure(url, options);
+  }
 
-    HttpUrl url = parseAnalyticsUrl(connectionString);
-    this.queryExecutor = new QueryExecutor(
-      new AnalyticsOkHttpClient(options, url, credential),
+  private static QueryExecutor newQueryExecutor(
+    ClusterOptions.Unmodifiable options,
+    HttpUrl url,
+    Credential credential
+  ) {
+    return new QueryExecutor(
+      new AnalyticsOkHttpClient(
+        options,
+        url,
+        credential
+      ),
       url,
       credential,
       options
     );
-
-    warnIfConfigurationIsInsecure(url, options);
   }
 
   private static void warnIfConfigurationIsInsecure(
@@ -204,6 +217,27 @@ private static String lowerSnakeCaseToLowerCamelCase(String s) {
     return sb.toString();
   }
 
+  /**
+   * Sets the credential to use for future requests.
+   *
+   * @throws IllegalStateException if the given credential is of a different type than the current credential
+   * (username and password / client certificate).
+   */
+  public void credential(Credential newCredential) {
+    requireNonNull(newCredential);
+
+    Class<?> oldClass = this.credential.getClass();
+    Class<?> newClass = newCredential.getClass();
+    if (!newClass.equals(oldClass)) {
+      throw new IllegalStateException("Switching credential types at runtime is not supported; cannot switch from " + oldClass + " to " + newClass);
+    }
+
+    this.credential = requireNonNull(newCredential);
+    this.queryExecutor = newQueryExecutor(this.options, this.url, this.credential);
+
+    // Don't close the old query executor, because we don't want to interfere with in-flight requests.
+    // The OkHttp resources automatically release themselves after a period of inactivity.
+  }
 
   /**
    * Returns the database in this cluster with the given name.

couchbase-analytics-java-client/src/main/java/com/couchbase/analytics/client/java/Credential.java

@@ -19,9 +19,24 @@
 import com.couchbase.analytics.client.java.internal.ThreadSafe;
 import okhttp3.Credentials;
 import okhttp3.tls.HandshakeCertificates;
+import okhttp3.tls.HeldCertificate;
+import org.jspecify.annotations.Nullable;
 
+import java.io.InputStream;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.security.GeneralSecurityException;
+import java.security.KeyPair;
+import java.security.KeyStore;
+import java.security.PrivateKey;
+import java.security.cert.Certificate;
+import java.security.cert.X509Certificate;
+import java.util.ArrayList;
+import java.util.Enumeration;
+import java.util.List;
 import java.util.function.Supplier;
 
+import static com.couchbase.analytics.client.java.internal.utils.lang.CbCollections.listCopyOf;
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static java.util.Objects.requireNonNull;
 
@@ -30,61 +45,180 @@
  * <pre>
  * Credential.of(username, password)
  * </pre>
- * <p>
- * For advanced use cases involving dynamic credentials, see
- * {@link Credential#ofDynamic(Supplier)}.
+ * Alternatively, to use a client certificate:
+ * <pre>
+ * Credential.fromKeyStore(
+ *     Paths.get("/path/to/client-cert.p12"),
+ *     "password"
+ * )
+ * </pre>
+ *
+ * @see Cluster#credential(Credential)
  */
 @ThreadSafe
 public abstract class Credential {
 
+  private static class UsernameAndPassword extends Credential {
+    private final String authHeaderValue;
+
+    UsernameAndPassword(String username, String password) {
+      this.authHeaderValue = Credentials.basic(username, password, UTF_8);
+    }
+
+    @Override
+    String httpAuthorizationHeaderValue() {
+      return authHeaderValue;
+    }
+
+    @Override
+    void addHeldCertificate(HandshakeCertificates.Builder builder) {
+    }
+  }
+
+  private static class ClientCertificate extends Credential {
+    private final HeldCertificate heldCertificate;
+    private final List<X509Certificate> intermediates;
+
+    public ClientCertificate(HeldCertificate heldCertificate, List<X509Certificate> intermediates) {
+      this.heldCertificate = requireNonNull(heldCertificate);
+      this.intermediates = listCopyOf(intermediates);
+    }
+
+    @Override
+    @Nullable String httpAuthorizationHeaderValue() {
+      return null;
+    }
+
+    @Override
+    void addHeldCertificate(HandshakeCertificates.Builder builder) {
+      builder.heldCertificate(heldCertificate, intermediates.toArray(new X509Certificate[0]));
+    }
+  }
+
+  private static class Dynamic extends Credential {
+    private final Supplier<Credential> supplier;
+
+    public Dynamic(Supplier<Credential> supplier) {
+      this.supplier = requireNonNull(supplier);
+    }
+
+    @Override
+    @Nullable String httpAuthorizationHeaderValue() {
+      return supplier.get().httpAuthorizationHeaderValue();
+    }
+
+    @Override
+    void addHeldCertificate(HandshakeCertificates.Builder builder) {
+      supplier.get().addHeldCertificate(builder);
+    }
+  }
+
   /**
    * Returns a new instance that holds the given username and password.
    */
   public static Credential of(String username, String password) {
-    String authHeaderValue = Credentials.basic(username, password, UTF_8);
+    return new UsernameAndPassword(username, password);
+  }
+
+  /**
+   * Returns a new instance that holds a client certificate loaded from the specified PKCS#12 key store file.
+   * <p>
+   * The key store must have a single entry which must contain a private key and certificate chain.
+   * The same password must be used for integrity and encryption.
+   * <p>
+   * <b>TIP:</b>
+   * One way to create a suitable PKCS#12 file from a PEM-encoded private key and certificate
+   * is to concatenate the key and certificate into a file named "client-cert.pem", then run this command:
+   * <pre>
+   * openssl pkcs12 -export -in client-cert.pem -out client-cert.p12 -passout pass:password
+   * </pre>
+   * This creates a PKCS#12 file named "client-cert.p12" protected by the password "password".
+   *
+   * @param password for verifying key store integrity and decrypting the private key
+   */
+  public static Credential fromKeyStore(Path pkcs12Path, @Nullable String password) {
+    KeyStore keyStore = loadKeyStore(pkcs12Path, password);
+    return fromKeyStore(keyStore, password);
+  }
 
-    return new Credential() {
-      @Override
-      String httpAuthorizationHeaderValue() {
-        return authHeaderValue;
+  /**
+   * Returns a new instance that holds a client certificate loaded from the specified key store.
+   * <p>
+   * The key store must have a single entry which must contain a private key and certificate chain.
+   *
+   * @param password for decrypting the private key
+   */
+  public static Credential fromKeyStore(KeyStore keyStore, @Nullable String password) {
+    try {
+      List<String> aliases = toList(keyStore.aliases());
+      if (aliases.size() != 1) {
+        throw new IllegalArgumentException("Expected the key store to contain exactly one entry, but got aliases: " + aliases);
       }
+      String alias = aliases.get(0);
+
+      PrivateKey privateKey = (PrivateKey) keyStore.getKey(alias, password == null ? null : password.toCharArray());
+      Certificate[] chain = keyStore.getCertificateChain(alias);
+      X509Certificate userCert = (X509Certificate) chain[0];
+
+      HeldCertificate heldCertificate = new HeldCertificate(
+        new KeyPair(userCert.getPublicKey(), privateKey),
+        userCert
+      );
 
-      @Override
-      void addHeldCertificate(HandshakeCertificates.Builder builder) {
-        // noop
+      List<X509Certificate> intermediates = new ArrayList<>();
+      for (int i = 1; i < chain.length; i++) { // skip zero-th because that's the user's certificate
+        intermediates.add((X509Certificate) chain[i]);
       }
-    };
+
+      return new ClientCertificate(heldCertificate, intermediates);
+
+    } catch (ClassCastException | GeneralSecurityException e) {
+      throw new RuntimeException("Failed to read client certificate from key store.", e);
+    }
+  }
+
+  private static KeyStore loadKeyStore(Path keyStorePath, @Nullable String password) {
+    try (InputStream keyStoreInputStream = Files.newInputStream(keyStorePath)) {
+      final KeyStore store = KeyStore.getInstance(KeyStore.getDefaultType());
+      store.load(
+        keyStoreInputStream,
+        password != null ? password.toCharArray() : null
+      );
+      return store;
+    } catch (Exception ex) {
+      throw new RuntimeException("Failed to read key store.", ex);
+    }
+  }
+
+  private static <T> List<T> toList(Enumeration<T> e) {
+    List<T> result = new ArrayList<>();
+    while (e.hasMoreElements()) {
+      result.add(e.nextElement());
+    }
+    return result;
   }
 
   /**
    * Returns a new instance of a dynamic credential that invokes the given supplier
    * every time a credential is required.
    * <p>
    * This enables updating a credential without having to restart your application.
+   *
+   * @deprecated This method is not compatible with client certificate credentials.
+   * Instead, please update the credential by calling {@link Cluster#credential(Credential)}.
    */
+  @Deprecated
   public static Credential ofDynamic(Supplier<Credential> supplier) {
-    requireNonNull(supplier);
-
-    return new Credential() {
-      @Override
-      String httpAuthorizationHeaderValue() {
-        return supplier.get().httpAuthorizationHeaderValue();
-      }
-
-      @Override
-      void addHeldCertificate(HandshakeCertificates.Builder builder) {
-        supplier.get().addHeldCertificate(builder);
-      }
-    };
+    return new Dynamic(supplier);
   }
 
-  abstract String httpAuthorizationHeaderValue();
+  abstract @Nullable String httpAuthorizationHeaderValue();
 
   abstract void addHeldCertificate(HandshakeCertificates.Builder builder);
 
   /**
    * @see #of
-   * @see #ofDynamic
+   * @see #fromKeyStore
    */
   private Credential() {
   }

couchbase-analytics-java-client/src/main/java/com/couchbase/analytics/client/java/QueryExecutor.java

@@ -221,9 +221,13 @@ QueryMetadata executeStreamingQueryOnce(
     Request.Builder requestBuilder = new Request.Builder()
       .url(url)
       .header("User-Agent", userAgent)
-      .header("Authorization", credential.httpAuthorizationHeaderValue())
       .post(requestBody(query));
 
+    String authHeaderValue = credential.httpAuthorizationHeaderValue();
+    if (authHeaderValue != null) {
+      requestBuilder.header("Authorization", authHeaderValue);
+    }
+
     Request request = requestBuilder.build();
 
     OkHttpClient client = httpClient.clientWithTimeout(timeout);