Enables IAuthenticator's to return own AuthenticateMessage

Allows custom implementations of IAuthenticator to return their own
AuthenticateMessage based on ClientState information.

ClientState contains information about driver's name and version which
could be used to determine the contents of the AuthenticateMessage that
is sent back to the clients. This enables, for instance, returning
driver's known authenticator implementations (e.g. DseAuthenticator)
which enables SASL negotiation.

 patch by Tiago Alves; reviewed by Mick Semb Wever, Andy Tolbert for CASSANDRA-19984

CHANGES.txt

@@ -1,4 +1,5 @@
 5.0.2
+ * Enables IAuthenticator's to return own AuthenticateMessage (CASSANDRA-19984)
  * Use ParameterizedClass for all auth-related implementations (CASSANDRA-19946)
  * Correct out-of-date metrics and configuration documentation for SAI (CASSANDRA-19898)
 Merged from 4.1:

src/java/org/apache/cassandra/auth/IAuthenticator.java

@@ -24,6 +24,8 @@ import java.util.Set;
 
 import org.apache.cassandra.exceptions.AuthenticationException;
 import org.apache.cassandra.exceptions.ConfigurationException;
+import org.apache.cassandra.service.ClientState;
+import org.apache.cassandra.transport.messages.AuthenticateMessage;
 
 public interface IAuthenticator
 {
@@ -54,6 +56,17 @@ public interface IAuthenticator
      */
     void setup();
 
+    /**
+     * Allows custom authenticators to return their own {@link AuthenticateMessage} based on
+     * {@link ClientState} information. For example, this allows returning the FQCN of a driver's
+     * known authenticator (e.g. "com.datastax.bdp.cassandra.auth.DseAuthenticator") to enable
+     * SASL scheme negotiation.
+     */
+    default AuthenticateMessage getAuthenticateMessage(ClientState clientState)
+    {
+        return new AuthenticateMessage(getClass().getName());
+    }
+
     /**
      * Provide a SASL handler to perform authentication for an single connection. SASL
      * is a stateful protocol, so a new instance must be used for each authentication

src/java/org/apache/cassandra/transport/messages/StartupMessage.java

@@ -22,6 +22,7 @@ import java.util.Map;
 
 import io.netty.buffer.ByteBuf;
 
+import org.apache.cassandra.auth.IAuthenticator;
 import org.apache.cassandra.config.DatabaseDescriptor;
 import org.apache.cassandra.service.ClientState;
 import org.apache.cassandra.service.QueryState;
@@ -118,8 +119,9 @@ public class StartupMessage extends Message.Request
             clientState.setDriverVersion(options.get(DRIVER_VERSION));
         }
 
-        if (DatabaseDescriptor.getAuthenticator().requireAuthentication())
-            return new AuthenticateMessage(DatabaseDescriptor.getAuthenticator().getClass().getName());
+        IAuthenticator authenticator = DatabaseDescriptor.getAuthenticator();
+        if (authenticator.requireAuthentication())
+            return authenticator.getAuthenticateMessage(clientState);
         else
             return new ReadyMessage();
     }

test/unit/org/apache/cassandra/auth/CustomAuthenticatorTest.java

@@ -0,0 +1,89 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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
+ *
+ *     http://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.apache.cassandra.auth;
+
+import java.net.InetAddress;
+import java.util.Map;
+import java.util.Set;
+
+import org.junit.Test;
+
+import org.apache.cassandra.exceptions.AuthenticationException;
+import org.apache.cassandra.exceptions.ConfigurationException;
+import org.apache.cassandra.service.ClientState;
+import org.apache.cassandra.transport.messages.AuthenticateMessage;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+
+public class CustomAuthenticatorTest
+{
+    private static final String CUSTOM_AUTHENTICATOR_FQCN = "com.example.auth.CustomAuthenticator";
+
+    @Test
+    public void testCustomAuthenticator()
+    {
+        IAuthenticator authenticator = new CustomAuthenticator();
+
+        AuthenticateMessage message = authenticator.getAuthenticateMessage(ClientState.forInternalCalls());
+
+        assertThat(message.authenticator).isNotEqualTo(authenticator.getClass().getName());
+        assertThat(message.authenticator).isEqualTo(CUSTOM_AUTHENTICATOR_FQCN);
+    }
+
+    private static class CustomAuthenticator implements IAuthenticator
+    {
+        @Override
+        public boolean requireAuthentication()
+        {
+            return false;
+        }
+
+        @Override
+        public Set<? extends IResource> protectedResources()
+        {
+            return Set.of();
+        }
+
+        @Override
+        public void validateConfiguration() throws ConfigurationException {}
+
+        @Override
+        public void setup() {}
+
+        @Override
+        public AuthenticateMessage getAuthenticateMessage(ClientState clientState)
+        {
+            return new AuthenticateMessage(CUSTOM_AUTHENTICATOR_FQCN);
+        }
+
+
+        @Override
+        public SaslNegotiator newSaslNegotiator(InetAddress clientAddress)
+        {
+            return null;
+        }
+
+        @Override
+        public AuthenticatedUser legacyAuthenticate(Map<String, String> credentials) throws AuthenticationException
+        {
+            return null;
+        }
+    }
+}

test/unit/org/apache/cassandra/auth/PasswordAuthenticatorTest.java

@@ -40,6 +40,7 @@ import org.apache.cassandra.exceptions.AuthenticationException;
 import org.apache.cassandra.exceptions.ConfigurationException;
 import org.apache.cassandra.schema.SchemaConstants;
 import org.apache.cassandra.service.StorageService;
+import org.apache.cassandra.transport.messages.AuthenticateMessage;
 
 import static org.apache.cassandra.auth.AuthTestUtils.ALL_ROLES;
 import static org.apache.cassandra.auth.CassandraRoleManager.DEFAULT_SUPERUSER_PASSWORD;
@@ -47,6 +48,7 @@ import static org.apache.cassandra.auth.CassandraRoleManager.getGensaltLogRounds
 import static org.apache.cassandra.auth.PasswordAuthenticator.SaslNegotiator;
 import static org.apache.cassandra.auth.PasswordAuthenticator.checkpw;
 import static org.apache.cassandra.config.CassandraRelevantProperties.AUTH_BCRYPT_GENSALT_LOG2_ROUNDS;
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
@@ -198,4 +200,11 @@ public class PasswordAuthenticatorTest extends CQLTester
         Map<String, String> cacheEntries = authenticator.bulkLoader().get();
         assertTrue(cacheEntries.isEmpty());
     }
+
+    @Test
+    public void testDefaultAuthenticateMessage()
+    {
+        AuthenticateMessage authenticateMessage = authenticator.getAuthenticateMessage(null);
+        assertThat(authenticateMessage.authenticator).isEqualTo(PasswordAuthenticator.class.getName());
+    }
 }