Status

Current state: DISCUSS ACCEPTED

Voting thread: https://www.mail-archive.com/dev@kafka.apache.org/msg104580.html

Discussion thread: https://www.mail-archive.com/dev@kafka.apache.org/msg101011.html

JIRA:

PR: https://github.com/apache/kafka/pull/8338

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

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Making javax.net.ssl.SSLContext setup pluggable provides flexibility for providing Key Material, Secure Random implementation and configure Key/Trust managers in a custom way. Example: Apache HttpComponents and Netty SslContextBuilder. 

Hence we feel we should make SSLContext initialization pluggableHowever, Kafka configures the SSLEngine for Client and Server both modes. Hence according to existing code it would be useful to make SslEngineBuilder pluggable. That will provide us a way to configure SSLContext object in a flexible way and at the same time will allow creation of SSLEngine with Client/Server mode.

Public Interfaces

New configuration

ssl.contextengine.factory.class - This configuration will take class of the below interface's type and will be used to create javax.net.ssl.SSLContext SSLEngine object.

Default value will be as mentioned below.

final    public static final String SSL_CONTEXTENGINE_FACTORY_CLASS_CONFIG = "ssl.contextengine.factory.class";
final    public static final String DEFAULT_SSL_CONTEXT_ENGINE_FACTORY_CLASS = org.apache.kafka.common.security.ssl.DefaultSslEngineFactory.class.getCanonicalName();
    public static final String SSL_ENGINE_FACTORY_CLASS_DOC = "The class of type org.apache.kafka.common.security.ssl.DefaultSslContextFactory"auth.SslEngineFactory to provide SSLEngine objects. Default value is " + DEFAULT_SSL_ENGINE_FACTORY_CLASS;

Interface for

...

SslEngineFactory

Below is the interface suggested for this.

package org.apache.kafka.common.security.sslauth;

import org.apache.kafka.common.Configurable;

import javax.net.ssl.SSLContextSSLEngine;
import java.io.Closeable;
import java.security.KeyStore;
import java.util.Map;
import java.util.Set;

/**
 * Plugin interface for allowing creation of SSLEngine object in a custom way.
 * Example: You want to use custom way to load your key material and trust material needed for SSLContext.
 * However, keep in mind that this is complementary to the existing Java Security Provider's mechanism and not a competing
 * solution.
 */
public interface SslContextFactory SslEngineFactory extends Configurable, Closeable {

    /**
     * Returns SSLContext loaded by this factoryCreate a new SSLEngine object to be used by the client.
     *
     * @param peerHost               The peer host to use. This is used in client mode if endpoint validation is enabled.
     * @param peerPort               The peer port to use. This is a hint and not used for validation.
     * @param endpointIdentification Endpoint identification algorithm for client mode.
     * @return The new SSLEngine.
     */
    SSLContextSSLEngine getSSLContext(createClientSslEngine(String peerHost, int peerPort, String endpointIdentification);

    /**
     * Returns the currently used configurations by this object Create a new SSLEngine object to be used by the server.
     *
     * @param peerHost               The peer host to use. This is used in client mode if endpoint validation is enabled.
     * @param peerPort               The peer port to use. This is a hint and not used for validation.
     * @return The new SSLEngine.
     */
    SSLEngine createServerSslEngine(String Map<StringpeerHost, Object>int configs(peerPort);

 	/**
    /** * Returns true if SSLEngine needs to be rebuilt. This method will be called when reconfiguration is triggered on
     * Returns the reconfigurable configs used by this object. {@link org.apache.kafka.common.security.ssl.SslFactory}. Based on the <i>nextConfigs</i>, this method will
     * decide whether underlying SSLEngine object needs to be rebuilt. If this method returns true, the
     * @return {@link org.apache.kafka.common.security.ssl.SslFactory} will re-create instance of this object and run other
     * checks before deciding to use the new object for the <i>new incoming connection</i> requests.The existing connections
     * are  Set<String> reconfigurableConfigs();
not impacted by this and will not see any changes done as part of reconfiguration.
     *
    / ** <pre>
     * Returns true     Example: If the implementation depends on the file based key material it can check if the SSLContext needs to be rebuilt file is updated
     *     compared to the previous/last-loaded timestamp and return true.
     * </pre>
     *
     * @param nextConfigs       The configuration we want to use.
     * @return                  True only if the SSLContextunderlying SSLEngine object should be rebuilt.
     */
    boolean shouldRebuiltForshouldBeRebuilt(Map<String, Object> nextConfigs);

    /**
     * Returns the names of configs that may be reconfigured.
     */
    Set<String> reconfigurableConfigs();

    /**
     * Returns keystore.
     * @return
     */
    KeyStore keystore();

    /**
     * Returns truststore.
     * @return
     */
    KeyStore truststore();
}

Proposed Changes

Currently SslFactory.java uses SslEngineBuilder.java. Instead of that we will modify SslFactory.java to load a class configured via the new configuration 'ssl.engine.factory.class' and delegate the SSLEngine creation call to the implementation. 

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• SslEngineBuilder.java (functionality of SSLContext loading will be moved to DefaultSslContextFactoryDefaultSslEngineFactory.java and createEngine() method will move to SslFactory.java)

Which classes will be added?

• SslContextFactorySslEngineFactory.java Interface
• DefaultSslContextFactoryDefaultSslEngineFactory.java (mostly having code from existing SslEngineBuilder)

Which classes will be modified primarily?

• SslFactory.java
• Will host the createEngine() method from current SslEngineBuilder and will have mechanism to load the SslContextFactory implementation

How does configs get to the implementation class?

The configuration of Map will be passed to the implementation class via the constructorconfigure() method. See below example,

public DefaultSslContextFactory DefaultSslEngineFactory implements SslEngineFactory {
...
...
	/* Default empty argument constructor */

	/* implement configure() method */
    @Override
    public void configure(Map<String, ?> configs) {
    ...
    }
...
...
}

These configuration will be passed from SslFactory to the implementation of the SslContextFactory SslEngineFactory interface via reflection like below

public class SslFactory implement Reconfigurable {
...
...
     sslContextFactoryClass.getDeclaredConstructor(Map.class).newInstance(configs);
.private SslEngineFactory instantiateSslEngineFactory(Map<String, Object> configs) {
        @SuppressWarnings("unchecked")
        Class<? extends SslEngineFactory> sslEngineFactoryClass =
                (Class<? extends SslEngineFactory>) configs.get(SslConfigs.SSL_ENGINE_FACTORY_CLASS_CONFIG);
        SslEngineFactory sslEngineFactory = Utils.newInstance(sslEngineFactoryClass);
        sslEngineFactory.configure(configs);
        this.sslEngineFactoryConfig = configs;
        return sslEngineFactory;
    }
...
}

Support for reconfiguration of custom configs

By custom configs we mean the configs used by the SslContextFactorySslEngineFactory's implementation. Those configs does not have to be part of definition of Kafka configs since only the implementation class knows what are those. Kafka already supports custom configs so this should not be a new challenge. 

Other challenge

Currently reconfigurations are pushed from Kafka code base to the reconfigurable classes. However, depending upon SslContextFactory's implementation we could have some events/changes detected by the implementation first and we would need to trigger reconfiguration on SslFactory in order to get re-initialized!

Probably this could be achieved by passing listener to those implementation changes but this needs to be further explored

Compatibility, Deprecation, and Migration Plan

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Not applicable since old code behavior will be kept with default implementation of DefaultSslContextFactory DefaultSslEngineFactory and modification to SslFactory class.

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This is because currently SslFactory does certain validations which we want to keep separate and mandate those checks across any possible implementation of pluggable ssl context class. Also, once we start writing the reconfigurable classes we realize that we need two classes - 1) SslContextFactory SslEngineFactory implementation and 2) Container of the factory implementation. We believe that keeping SslFactory as Reconfigurable object and help reconfigure the underlying SslContextFactory SslEngineFactory will simplify the implementations of SslContextFactorySslEngineFactory.

Also, we rejected to make SslContextFactory SslEngineFactory extend the Reconfigurable interface due to following reason,

There will be good amount of state in the SslContextFactorySslEngineFactory's implementation (as it will be similar to the current SslEngineBuilder class). We believe that making SSLContext creation and SSLEngine object's configuration pluggable is worth to allow SSL experts to write their own implementation having the SSL domain knowledge and keep them free of knowing much about Kafka's reconfigurability - example: Apache HttpComponents. We prefer SslFactory class to do what it is doing right now and keep the responsibility of re-creating underlying SslContextFactory SslEngineFactory object based on the configurations specified by the SslContextFactory's implementation.

Creating builder for SSLContext

Creating We could create a builder for SSLContext object and have a mechanism to configure SSLEngine object for client/server mode non-pluggable. However, creating a builder interface with options to build SSLContext will need to have method(s) to allow keys/trusted-certs. It will also require us to have 'key-password' as input for the keystore. In the current Kafka implementation it requires the password to be configured in the plaintext via 'ssl.key.password', 'ssl.keystore.password' and 'ssl.truststore.password'. If we need to customize how the password is loaded, due to security reasons, this approach will not work since some other mechanism for making password pluggable (See KIP-76 Enable getting password from executable rather than passing as plaintext in config files AND KIP-486: Support custom way to load KeyStore and TrustStore) need to be devised which will add more ssl related configurations to Kafka.

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