Status

Current state: "Under DiscussionAccepted"

Discussion thread: here

JIRA:

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

...

1. Define a new Java interface for authorizer in 'clients' module in the package 'org.apache.kafka.server' similar to other server-side pluggable classes.
2. KIP-4 has added ACL-related classes in the package org.apache.kafka.common (e.g. ResourcePattern and AccessControlEntry) to support ACL management using AdminClient. We will attempt to reuse these classes wherever possible.
3. Deprecate but retain existing Scala authorizer API for backward compatibility to ensure that existing custom authorizers can be used with new brokers.
4. Provide context about the request to authorizers to enable context-specific logic based on security protocol or listener to be applied to authorization.
5. Provide additional context about the request including ApiKey and correlation id from the request header since these are useful for matching debug-level authorization logs with corresponding request logs.
6. For ACL updates, provide request context including principal requesting the update and the listener on which request arrived to enable additional validation.
7. Return individual responses for each access control entry update when multiple entries of a resource are updated. At the moment, we update the ZooKeeper node for a resource pattern multiple times when a request adds or removes multiple entries for a resource in a single update request. Since it is a common usage pattern to add or remove multiple access control entries while updating ACLs for a resource, batched updates will be supported to enable a single atomic update for each resource pattern.
8. Provide authorization mode usage flag to authorizers to enable authorization logs to indicate attempts to access unauthorized resources. Kafka brokers log denied operations at INFO level and allowed operations at DEBUG level with the expectation that denied operations are rare and indicate erroneous or malicious use of the system. But we currently have several uses of Authorizer#authorize for filtering accessible resources or operations, for example for regex subscription. These fill up authorization logs with denied log entries, making these logs unusable for determining actual attempts to access resources by users who don’t have appropriate permissions. Authorization mode Audit flag will enable the authorizer to determine the severity of denied access.
9. For authorizers that don’t store metadata in ZooKeeper, ensure that authorizer metadata for each listener is available before starting up the listener. This enables different authorization metadata stores for different listeners.
10. Rewrite Add a new out-of-the-box authorizer class SimpleAclAuthorizer to implement that implements the new authorizer interface, making use of the features supported by the new API.
11. Retain existing audit log entry format in SimpleAclAuthorizer to ensure that tools that parse these logs continue to work.
12. Enable Authorizer implementations to make use of additional Kafka interfaces similar to other pluggable callbacks. Authorizers can implement org.apache.kafka.common.Reconfigurable  to support dynamic reconfiguration without restarting the broker. Authorizers implementing org.apache.kafka.common.ClusterResourceListener will will also be provided cluster id which may be included in logs or used to support centralized ACL storage.
13. Enable asynchronous ACL updates to avoid blocking broker request threads when ACLs are updated in a remote store (e.g. a database).

Public Interfaces

Authorizer Configuration

A new The existing configuration option `authorizer.class` .name` will be introduced extended to configure a support broker authorizer authorizers using the new Java interface org.apache.kafka.server.authorizer.Authorizer . The existing config `authorizer.class.name` will be deprecated, but will continue to support authorizers using the existing Scala trait kafka.security.auth.Authorizer.

New configuration option:

...

...

Authorizer API

The new Java Authorizer interface and its supporting classes are shown below:

package org.apache.kafka.server.authorizer;

import java.io.Closeable;
import java.util.List;
import java.util.Map;
import java.util.concurrent.CompletableFutureCompletionStage;
import org.apache.kafka.common.ClusterResourceConfigurable;
import org.apache.kafka.common.ConfigurableEndpoint;
import org.apache.kafka.common.acl.AclBinding;
import org.apache.kafka.common.acl.AclBindingFilter;
import org.apache.kafka.common.annotation.InterfaceStability;
import org.apache.kafka.common.security.auth.SecurityProtocol;
import org.apache.kafka.common.KafkaRequestContext;

/**
 *
 * Pluggable authorizer interface for Kafka brokers.
 *
 * Startup sequence in brokers:
 * <ol>
 *   <li>Broker creates authorizer instance if configured in `authorizer.class` or `authorizer.class.name`.</li>
 *   <li>Broker configures and starts authorizer instance. Authorizer implementation starts loading its metadata.</li>
 *   <li>Broker starts SocketServer to accept connections and process requests.</li>
 *   <li>For each listener, SocketServer waits for authorization metadata to be available in the
 *       authorizer before accepting connections. The future returned by {@link #start(ClusterResource, MapAuthorizerServerInfo)} )}
 *       must return only when authorizer is ready to authorize requests on the listener.</li>
 *   <li>Broker accepts connections. For each connection, broker performs authentication and then accepts Kafka requests.
 *       For each request, broker invokes {@link #authorize(KafkaRequestContextAuthorizableRequestContext, List)} to authorize
 *       actions performed by the request.</li>
 * </ol>
 *
 * Authorizer implementation class may optionally implement @{@link org.apache.kafka.common.Reconfigurable}
 * to enable dynamic reconfiguration without restarting the broker.
 * <p>
 * <b>Thread<b>Threading safetymodel:</b> All
 * <ul>
 *   <li>All authorizer operations including authorization and ACL updates must be thread-safe.
 * </p>li>
 */
@InterfaceStability.Evolving
public interface Authorizer extends Configurable, Closeable {

    /**
     * Starts loading authorization metadata and returns futures that can be used to wait until
   <li>ACL update methods are asynchronous. Implementations with low update latency may return a
 *       completed future using {@link java.util.concurrent.CompletableFuture#completedFuture(Object)}.
 *       *This metadataensures that forthe authorizingrequest requestswill onbe eachhandled listenersynchronously isby available.the Eachcaller listenerwithout willusing bea
 *    * started only afterpurgatory itsto metadatawait isfor availablethe andresult. authorizerIf isACL readyupdates torequire startremote authorizing
communication which may block,
  * requests on that listener.
   return a *
future that is completed asynchronously *when @paramthe clusterResourceremote Clusteroperation metadatacompletes. forThis theenables
 Kafka* cluster
     * @paramthe listenerscaller Listenerto namesprocess withother theirrequests securityon protocols
the request threads without blocking.</li>
 * @return  CompletableFutures<li>Any forthreads eachor listenerthread thatpools completesused whenfor authorizerprocessing isremote readyoperations to
asynchronously can be started during
 *       {@link  start authorizing requests on that listener. Returned map contains one future
     *         for each listener name in the input `listeners` map.
     */
    Map<String, CompletableFuture<Void>> start(ClusterResource clusterResource,#start(AuthorizerServerInfo)}. These threads must be shutdown during {@link Authorizer#close()}.</li>
 * </ul>
 * </p>
 */
@InterfaceStability.Evolving
public interface Authorizer extends Configurable, Closeable {

    /**
     * Starts loading authorization metadata and returns futures that can be used to wait until
     * metadata for authorizing requests on each listener is available. Each listener will be
     * started only after its metadata is available and authorizer is ready to start authorizing
     * requests on that listener.
 Map<String, SecurityProtocol> listeners);

    /**
     * Authorizes@param serverInfo theMetadata specifiedfor action.the Additionalbroker metadataincluding forbroker theid actionand islistener specifiedendpoints
     * in `requestContext`.
     *@return CompletionStage for each endpoint that completes when authorizer is ready to
     * @param requestContext Request context    including requeststart type,authorizing securityrequests protocolon andthat listener name.
     */
 @param  actions ActionsMap<Endpoint, being? authorizedextends includingCompletionStage<Void>> resource and operation for each actionstart(AuthorizerServerInfo serverInfo);

    /**
     * Authorizes @returnthe Listspecified ofaction. authorizationAdditional resultsmetadata for eachthe action inis specified
 the same order as the* providedin actions`requestContext`.
     */ <p>
    List<AuthorizationResult> authorize(KafkaRequestContext requestContext, List<Action> actions);

    /**
     * Creates new ACL bindings.
     ** This is a synchronous API designed for use with locally cached ACLs. Since this method is invoked on the
     * @paramrequest requestContextthread Requestwhile contextprocessing ifeach therequest, ACLimplementations isof beingthis createdmethod byshould a broker to handleavoid time-consuming
     * remote communication that may block request threads.
 a client request to create*
 ACLs. This may be null* if@param ACLsrequestContext areRequest createdcontext directlyincluding inrequest ZooKeeper
type, security protocol and  *        using AclCommand.listener name
     * @param aclBindingsactions Actions ACLbeing bindingsauthorized toincluding create
resource and operation for each *action
     * @return Create resultList of authorization results for each ACLaction binding in the same order as in the inputprovided listactions
     */
    List<AclCreateResult>List<AuthorizationResult> createAclsauthorize(KafkaRequestContextAuthorizableRequestContext requestContext, List<AclBinding>List<Action> aclBindingsactions);

    /**
     * DeletesCreates allnew ACL bindings.
 that  match the provided* filters.<p>
     *
 This is an asynchronous *API @paramthat requestContextenables Requestthe contextcaller ifto theavoid ACLblocking isduring beingthe deletedupdate. byImplementations a broker to handleof this
     * API can return completed futures using  a client request to delete ACLs. This may be null if ACLs are deleted directly in ZooKeeper{@link java.util.concurrent.CompletableFuture#completedFuture(Object)}
     * to process the update synchronously on the request thread.
     *
     * @param requestContext using AclCommand.
     * @param aclBindingFilters Filters to match ACL bindings that are to be deleted
Request context if the ACL is being created by a broker to handle
     *       *
 a client request to *create @returnACLs. DeleteThis resultmay forbe eachnull filterif inACLs theare samecreated orderdirectly as in the input list.ZooKeeper
     *        using EachAclCommand.
 result indicates which ACL  * @param aclBindings ACL bindings wereto actuallycreate
 deleted as well as any*
     * @return Create result for each ACL binding in bindingsthe thatsame matchedorder butas couldin notthe beinput deletedlist.
 Each    */result
    List<AclDeleteResult> deleteAcls(KafkaRequestContext* requestContext, List<AclBindingFilter> aclBindingFilters);

    /**
  is returned as *a ReturnsCompletionStage ACLthat bindingscompletes whichwhen matchthe theresult providedis filteravailable.
     */
    List<? extends CompletionStage<AclCreateResult>> createAcls(AuthorizableRequestContext requestContext, List<AclBinding> aclBindings);

    /* @return Iterator for*
     * Deletes all ACL bindings, whichthat maymatch bethe populatedprovided lazilyfilters.
     */ <p>
     * This  Iterable<AclBinding> acls(AclBindingFilter filter);
}

Request context will provided to authorizers using a new interface KafkaRequestContext. The existing class org.apache.kafka.common.requests.RequestContext will implement this interface.

package org.apache.kafka.common;

import java.net.InetAddress;
import org.apache.kafka.common.annotation.InterfaceStability;
import org.apache.kafka.common.security.auth.KafkaPrincipal;
import org.apache.kafka.common.security.auth.SecurityProtocol;

/**
 * Request context interface that provides data from request header as well as connection
 * and authentication information to plugins.
 */
@InterfaceStability.Evolving
public interface KafkaRequestContext {

    /**is an asynchronous API that enables the caller to avoid blocking during the update. Implementations of this
     * API can return completed futures using {@link java.util.concurrent.CompletableFuture#completedFuture(Object)}
     * to process the update synchronously on the request thread.
     *
     * @param requestContext Request context if the ACL is being deleted by a broker to handle
     * Returns name of listener on which request wasa received.
client request to delete  */
    String listenerName();

    /**ACLs. This may be null if ACLs are deleted directly in ZooKeeper
     * Returns the security protocol for the listener on which request was receivedusing AclCommand.
     */
    SecurityProtocol securityProtocol();

 @param aclBindingFilters Filters to match ACL bindings that are to be deleted
     /**
     * Returns@return authenticatedDelete principalresult for each filter in the connectionsame order onas whichin requestthe wasinput receivedlist.
     */
     KafkaPrincipal principal();

   Each /**
result indicates which ACL bindings *were Returnsactually clientdeleted IPas addresswell fromas whichany
 request was sent.
     */
    InetAddress clientAddress();

    /**
bindings that matched but could *not Returnsbe thedeleted. requestEach typeresult (ApiKey)is fromreturned theas requesta
 header. For fetch requests,
 *    * the metrics names FetchFollower andCompletionStage FetchConsumerthat willcompletes bewhen usedthe toresult distinguishis betweenavailable.
     */
 replica fetch requests andList<? clientextends fetch requests.
     */
    String requestType(CompletionStage<AclDeleteResult>> deleteAcls(AuthorizableRequestContext requestContext, List<AclBindingFilter> aclBindingFilters);

    /**
     * Returns theACL requestbindings versionwhich frommatch the requestprovided headerfilter.
     */ <p>
    int requestVersion();

    /**
     * Returns the client id from the request header. * This is a synchronous API designed for use with locally cached ACLs. This method is invoked on the request
     */
 thread while processing String clientId();

    /*DescribeAcls requests and should avoid time-consuming remote communication that may
     * block request threads.
     *
     * Returns the correlation id from the request header@return Iterator for ACL bindings, which may be populated lazily.
     */
    intIterable<AclBinding> correlationIdacls(AclBindingFilter filter);
}

Action  provides details of the action being authorized including resource and operation. Additional context including authorization mode are also included, enabling access violation to be distinguished from resource filtering or optional ACLsRequest context will be provided to authorizers using a new interface AuthorizableRequestContext. The existing class org.apache.kafka.common.requests.RequestContext will implement this interface. New methods may be added to this interface in future, so mock implementations using this interface should adapt to these changes.

package org.apache.kafka.server.authorizer;

import orgjava.apache.kafka.common.acl.AclOperationnet.InetAddress;
import org.apache.kafka.common.annotation.InterfaceStability;
import org.apache.kafka.common.security.resourceauth.PatternTypeKafkaPrincipal;
import org.apache.kafka.common.security.resourceauth.ResourcePatternSecurityProtocol;
import org.apache.kafka.common.resource.ResourceType;

/**
 * Request context interface that provides data from request header as well as connection
 * and authentication information to plugins.
 */
@InterfaceStability.Evolving
public classinterface ActionAuthorizableRequestContext {

    private final ResourcePattern resourcePattern;/**
    private final* AclOperationReturns operation;
name of listener on privatewhich finalrequest AuthorizationModewas authorizationMode;received.
    private final int count */
    String listenerName();

    public Action(AclOperation operation,/**
     * Returns the security protocol for the listener on which request was received.
 ResourceType resourceType,
   */
    SecurityProtocol securityProtocol();

    /**
     * StringReturns resourceName,
authenticated principal for the connection on which request was received.
     */
    AuthorizationMode authorizationMode,KafkaPrincipal principal();

    /**
     * Returns client IP address from which request  int count) {was sent.
     */
   this.operation =InetAddress operationclientAddress();

    /**
    this.resourcePattern =* new ResourcePattern(resourceType, resourceName, PatternType.LITERAL);
        this.authorizationMode = authorizationMode;16-bit API key of the request from the request header. See
     * https://kafka.apache.org/protocol#protocol_api_keys for this.count = count;request types.
     */
    } int requestType();

    /**
     * ResourceReturns the onrequest whichversion actionfrom isthe beingrequest performedheader.
     */
    publicint ResourcePattern resourcePatternrequestVersion() {;

        return resourcePattern;/**
    }

    /**
 Returns the client id *from Operationthe beingrequest performedheader.
     */
    publicString AclOperation operationclientId() {;

        return operation;
    }

    /**/**
     * AuthorizationReturns modethe tocorrelation enableid authorizationfrom logsthe to distinguish between attempts
     * to access unauthorized resources and other filtering operations performed by the brokerrequest header.
     */
    publicint AuthorizationMode authorizationModecorrelationId() {
        return authorizationMode;
    }

    /**
     * Number of times the authorization result is used. For example, a single topic
     * authorization result may be used with `count` partitions of the topic within a single
     * request;
}

AuthorizerServerInfo provides runtime broker configuration to authorization plugins including broker id, cluster id and endpoint information. New methods may be added to this interface in future, so mock implementations using this interface should adapt to these changes.

package org.apache.kafka.server.authorizer;

import java.util.Collection;
import org.apache.kafka.common.ClusterResource;
import org.apache.kafka.common.Endpoint;
import org.apache.kafka.common.annotation.InterfaceStability;

/**
 * Runtime broker configuration metadata provided to authorizers during start up.
 */
@InterfaceStability.Evolving
public interface AuthorizerServerInfo {

    /**
     * Returns cluster metadata for the broker running this authorizer including cluster id.
     */
    publicClusterResource int countclusterResource() {;

    /**
    return count;
* Returns broker  }

Authorization Mode:

package org.apache.kafka.server.authorizer;

public enum AuthorizationMode {
    /**id. This may be a generated broker id if `broker.id` was not configured.
     */
 Access was requested to resource. If authorization result is ALLOWED, access is granted to
     * the resource to perform the request. If DENIED, request is failed with authorization failureint brokerId();

    /**
     * Returns endpoints for all listeners including the advertised host and port to which
     * the listener is bound.
     */
     MANDATORY,Collection<Endpoint> endpoints();

    /**
     * AccessReturns wasthe requested to resourceinter-broker endpoint. IfThis authorization result is ALLOWED, access is granted to
     *one of the resourceendpoints toreturned performby the request. If DENIED, alternative authorization rules are applied{@link #endpoints()}.
     * to determine if access is allowed./
     */
    OPTIONAL,

    /**
     * Access was requested to authorized resources (e.g. to subscribe to regex pattern).
     * Request is performed on resources whose authorization result is ALLOWED and the rest of
     * the resources are filtered out.
     */
    FILTER,

    /**
     * Request to list authorized operations. No access is actually performed by this request
     * based on the authorization result.
     */
    LIST_AUTHORIZED
}

Authorize method returns individual allowed/denied results for every action. ACL create and delete operations will return any exceptions from each access control entry requested.

Endpoint interBrokerEndpoint();
}

Endpoint is added as a common class so that it may be reused in several places in the code where we use this abstraction.

package org.apache.kafka.common;

import java.util.Objects;
import java.util.Optional;

import org.apache.kafka.common.annotation.InterfaceStability;
import org.apache.kafka.common.security.auth.SecurityProtocol;

/**
 * Represents a broker endpoint.
 */

@InterfaceStability.Evolving
public class Endpoint {

    private final String listenerName;
    private final SecurityProtocol securityProtocol;
    private final String host;
    private final int port;

    public Endpoint(String listenerName, SecurityProtocol securityProtocol, String host, int port) {
        this.listenerName = listenerName;
        this.securityProtocol = securityProtocol;
        this.host = host;
        this.port = port;
    }

    /**
     * Returns the listener name of this endpoint. This is non-empty for endpoints provided
     * to broker plugins, but may be empty when used in clients.
     */
    public Optional<String> listenerName(

package org.apache.kafka.server.authorizer;

public enum AuthorizationResult {
    ALLOWED,
    DENIED
}

import org.apache.kafka.common.annotation.InterfaceStability;
@InterfaceStability.Evolving
public class AclCreateResult {
    private final Throwable exception;

    public AclCreateResult() {
        this(null);
    }

    public AclCreateResult(Throwable exception) {
        this.exception = exceptionreturn Optional.ofNullable(listenerName);
    }

    /**
     * Returns anythe exceptionsecurity duringprotocol create.of If exception is null, the request has succeededthis endpoint.
     */
    public ThrowableSecurityProtocol exceptionsecurityProtocol() {
        return exceptionsecurityProtocol;
    }

    /**
     * Returns advertised truehost ifname theof requestthis failedendpoint.
     */
    public booleanString failedhost() {
        return exception != nullhost;
    }
}

package org.apache.kafka.server.authorizer;

import java.util.Collections;
import java.util.Set;
import org.apache.kafka.common.acl.AclBinding;
import org.apache.kafka.common.errors.ApiException;

public class AclDeleteResult {
    private final ApiException exception;
    /**
     * Returns the port to which the listener is bound.
    private final Set<DeleteResult> deleteResults;

 */
    public AclDeleteResult(ApiException exceptionint port() {
        this(Collections.emptySet(), exception)return port;
    }

    public AclDeleteResult(Set<DeleteResult> deleteResults@Override
    public boolean equals(Object o) {
        this(deleteResults, null);if (this == o) {
    }

    private AclDeleteResult(Set<DeleteResult> deleteResults, ApiException exception)return {true;
        this.deleteResults}
 = deleteResults;
      if  this.exception = exception;(!(o instanceof Endpoint)) {
    }

    /**
    return *false;
 Returns any exception while attempting to match ACL}

 filter to delete   ACLs.
  Endpoint that  */= (Endpoint) o;
    public    ApiExceptionreturn exception(Objects.equals(this.listenerName, that.listenerName) {&&
        return exception;
    }

    /**Objects.equals(this.securityProtocol, that.securityProtocol) &&
     * Returns delete result for each matching ACL binding. Objects.equals(this.host, that.host) &&
     */
    public Set<DeleteResult> deleteResults() {
        return deleteResults;
 this.port == that.port;

    }


    /**@Override
    public *int Delete result for each ACL binding that matched a delete filter.
     */hashCode() {
        return Objects.hash(listenerName, securityProtocol, host, port);
    public class DeleteResult {}

    @Override
    privatepublic finalString AclBinding aclBinding;toString() {
        private final ApiException exception;

return "Endpoint(" +
        public DeleteResult(AclBinding aclBinding) {
 "listenerName='" + listenerName + '\'' +
      this(aclBinding, null);
     ", securityProtocol=" + securityProtocol }
+
        public DeleteResult(AclBinding aclBinding, ApiException exception) {
     ", host='" + host + '\'' +
       this.aclBinding = aclBinding;
   ", port=" +       this.exception = exception;port +
        }

        /**
    ')';
     * Returns ACL binding that matched the delete filter. {@link #deleted()} indicates if
         * the binding was deleted.
         */
        public AclBinding aclBinding() {
            return aclBinding
}

Action  provides details of the action being authorized including resource and operation. Additional context including audit flag indicating authorization usage are also included, enabling access violation to be distinguished from resource filtering or optional ACLs.

package org.apache.kafka.server.authorizer;

import java.util.Objects;
import org.apache.kafka.common.acl.AclOperation;
import org.apache.kafka.common.annotation.InterfaceStability;
import org.apache.kafka.common.resource.PatternType;
import org.apache.kafka.common.resource.ResourcePattern;
import org.apache.kafka.common.resource.ResourceType;

@InterfaceStability.Evolving
public class Action {

    private final ResourcePattern resourcePattern;
    private final AclOperation operation;
    private final int  }resourceReferenceCount;

    private final   /**boolean logIfAllowed;
    private final boolean logIfDenied;

  * Returns exceptionpublic that resulted in failure to delete ACL binding.Action(AclOperation operation,
         */
        public ApiException exception() {
 ResourcePattern resourcePattern,
           return exception;
       int }resourceReferenceCount,

        /**
         * Returns true if ACL binding was deleted, false otherwise.boolean logIfAllowed,
         */
        public boolean deleted(logIfDenied) {
        this.operation = operation;
     return exception == null;
   this.resourcePattern = resourcePattern;
        this.logIfAllowed = logIfAllowed;
        this.logIfDenied = logIfDenied;
        this.resourceReferenceCount = resourceReferenceCount;
    }

    }
}

Proposed Changes

Deprecate existing Scala Authorizer

kafka.security.auth.Authorizer will be deprecated along with all the supporting Scala classes including Resource, Operations and ResourceTypes. A new AuthorizerWrapper class will be introduced to wrap implementations using the Scala trait into the new Java interface. All usage of Authorizer (e.g. in KafkaApis) will be replaced with the new authorizer interface.

SimpleAclAuthorizer

SimpleAclAuthorizer will be updated to implement the new interface, making use of the additional request context available to improve authorization logging. This enables the authorizer to be used with the new config 'authorizer.class'. SimpleAclAuthorizer will remain a Scala class in `core`.  SimpleAclAuthorizer will continue to implement the old Scala Authorizer trait so that it can continue to be used with the old config 'authorizer.class.name', Internally, it will be handled as the new interface without a wrapper regardless of which config was used.

Optional Interfaces

ClusterResourceListener

kafka.server.KafkaServer will be updated to provide cluster-id to the configured authorizer if it implements org.apache.kafka.common.ClusterResourceListener interface. This will enable the authorizer to include cluster-id in logs and to use centralized ACLs if required.

Reconfigurable

kafka.server.DynamicBrokerConfig will be updated to support dynamic update of authorizers which implement org.apache.kafka.common.Reconfigurable. Authorizer implementations can react to dynamic updates of any of its configs including custom configs, avoiding broker restarts to update configs.

Compatibility, Deprecation, and Migration Plan

What impact (if any) will there be on existing users?

Existing authorizer interfaces and classes are being deprecated, but not removed. We will continue to support the old config with the old API to ensure that existing users are not impacted.

If we are changing behavior how will we phase out the older behavior?

We are deprecating the existing config `authorizer.class.name` and the existing Scala authorizer API. These will be removed in a future release, but will continue to be supported for backward compatibility until then. Until the old authorizer is removed, no config changes are required during upgrade.

Test Plan

All the existing integration and system tests will be updated to use the new config and the new authorization class. Unit tests will be added for testing the new methods and parameters being introduced in this KIP. An additional integration test will be added to test authorizers using the old Scala API.  

Rejected Alternatives

Description of Authorizer as proposed in KIP-50

KIP-50 proposes to return a textual description of the authorizer that can be used in tools like AclCommand. Since we don’t support returning a description using AdminClient and none of the other pluggable APIs have similar support, this KIP does not add a method to return authorizer description.

Separate authorizers for each listener

/**
     * Resource on which action is being performed.
     */
    public ResourcePattern resourcePattern() {
        return resourcePattern;
    }

    /**
     * Operation being performed.
     */
    public AclOperation operation() {
        return operation;
    }

    /**
     * Indicates if audit logs tracking ALLOWED access should include this action if result is
     * ALLOWED. The flag is true if access to a resource is granted while processing the request as a
     * result of this authorization. The flag is false only for requests used to describe access where
     * no operation on the resource is actually performed based on the authorization result.
     */
    public boolean logIfAllowed() {
        return logIfAllowed;
    }

    /**
     * Indicates if audit logs tracking DENIED access should include this action if result is
     * DENIED. The flag is true if access to a resource was explicitly requested and request
     * is denied as a result of this authorization request. The flag is false if request was
     * filtering out authorized resources (e.g. to subscribe to regex pattern). The flag is also
     * false if this is an optional authorization where an alternative resource authorization is
     * applied if this fails (e.g. Cluster:Create which is subsequently overridden by Topic:Create).
     */
    public boolean logIfDenied() {
        return logIfDenied;
    }

    /**
     * Number of times the resource being authorized is referenced within the request. For example, a single
     * request may reference `n` topic partitions of the same topic. Brokers will authorize the topic once
     * with `resourceReferenceCount=n`. Authorizers may include the count in audit logs.
     */
    public int resourceReferenceCount() {
        return resourceReferenceCount;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (!(o instanceof Action)) {
            return false;
        }

        Action that = (Action) o;
        return Objects.equals(this.resourcePattern, that.resourcePattern) &&
            Objects.equals(this.operation, that.operation) &&
            this.resourceReferenceCount == that.resourceReferenceCount &&
            this.logIfAllowed == that.logIfAllowed &&
            this.logIfDenied == that.logIfDenied;

    }

    @Override
    public int hashCode() {
        return Objects.hash(resourcePattern, operation, resourceReferenceCount, logIfAllowed, logIfDenied);
    }

    @Override
    public String toString() {
        return "Action(" +
            ", resourcePattern='" + resourcePattern + '\'' +
            ", operation='" + operation + '\'' +
            ", resourceReferenceCount='" + resourceReferenceCount + '\'' +
            ", logIfAllowed='" + logIfAllowed + '\'' +
            ", logIfDenied='" + logIfDenied + '\'' +
            ')';
    }
}

Authorize method returns individual allowed/denied results for every action.

package org.apache.kafka.server.authorizer;

public enum AuthorizationResult {
    ALLOWED,
    DENIED
}

ACL create operation returns any exception from each ACL binding requested.

package org.apache.kafka.server.authorizer;

import java.util.Optional;
import org.apache.kafka.common.annotation.InterfaceStability;
import org.apache.kafka.common.errors.ApiException;

@InterfaceStability.Evolving
public class AclCreateResult {
    public static final AclCreateResult SUCCESS = new AclCreateResult();

    private final ApiException exception;

    private AclCreateResult() {
        this(null);
    }

    public AclCreateResult(ApiException exception) {
        this.exception = exception;
    }

    /**
     * Returns any exception during create. If exception is empty, the request has succeeded.
     */
    public Optional<ApiException> exception() {
        return exception == null ? Optional.empty() : Optional.of(exception);
    }
}

ACL delete operation returns any exception from each ACL filter requested. Matching ACL bindings for each filter are returned along with any delete failure.

package org.apache.kafka.server.authorizer;

import java.util.Collections;
import java.util.Collection;
import java.util.Optional;
import org.apache.kafka.common.acl.AclBinding;
import org.apache.kafka.common.annotation.InterfaceStability;
import org.apache.kafka.common.errors.ApiException;

@InterfaceStability.Evolving
public class AclDeleteResult {
    private final ApiException exception;
    private final Collection<AclBindingDeleteResult> aclBindingDeleteResults;

    public AclDeleteResult(ApiException exception) {
        this(Collections.emptySet(), exception);
    }

    public AclDeleteResult(Collection<AclBindingDeleteResult> deleteResults) {
        this(deleteResults, null);
    }

    private AclDeleteResult(Collection<AclBindingDeleteResult> deleteResults, ApiException exception) {
        this.aclBindingDeleteResults = deleteResults;
        this.exception = exception;
    }

    /**
     * Returns any exception while attempting to match ACL filter to delete ACLs.
     */
    public Optional<ApiException> exception() {
        return exception == null ? Optional.empty() : Optional.of(exception);
    }

    /**
     * Returns delete result for each matching ACL binding.
     */
    public Collection<AclBindingDeleteResult> aclBindingDeleteResults() {
        return aclBindingDeleteResults;
    }


    /**
     * Delete result for each ACL binding that matched a delete filter.
     */
    public static class AclBindingDeleteResult {
        private final AclBinding aclBinding;
        private final ApiException exception;

        public AclBindingDeleteResult(AclBinding aclBinding) {
            this(aclBinding, null);
        }

        public AclBindingDeleteResult(AclBinding aclBinding, ApiException exception) {
            this.aclBinding = aclBinding;
            this.exception = exception;
        }

        /**
         * Returns ACL binding that matched the delete filter. {@link #deleted()} indicates if
         * the binding was deleted.
         */
        public AclBinding aclBinding() {
            return aclBinding;
        }

        /**
         * Returns any exception that resulted in failure to delete ACL binding.
         */
        public Optional<ApiException> exception() {
            return exception == null ? Optional.empty() : Optional.of(exception);
        }
    }
}

Proposed Changes

Asynchronous update requests

kafka.server.KafkaApis will be updated to handle CreateAcls and DeleteAcls requests asynchronously using a purgatory. If Authorizer.createAcls or Authorizer.deleteAcls returns any ComplettionStage that is not complete, the request will be added to a purgatory and completed when all the stages complete. Authorizer implementations with low latency updates may continue to update synchronously and return a completed future. These requests will be completed in-line and will not be added to the purgatory.

Asynchronous updates are useful for Authorizer implementations that use external stores for ACLs, for example a database. Async handling of update requests will enable Kafka brokers to handle database outages without blocking request threads. As many databases now support async APIs (https://dev.mysql.com/doc/x-devapi-userguide/en/synchronous-vs-asynchronous-execution.html, https://blogs.oracle.com/java/jdbc-next:-a-new-asynchronous-api-for-connecting-to-a-database), async update API enables authorizers to take advantage of these APIs.

Purgatory metrics will be added for ACL updates, consistent with metrics from other purgatories. Two new metrics will be added:

• kafka.server:type=DelayedOperationPurgatory,name=NumDelayedOperations,delayedOperation=acl-update
• kafka.server:type=DelayedOperationPurgatory,name=PurgatorySize,delayedOperation=acl-update

In addition to these metrics, existing request metrics for CreateAcls and DeleteAcls can be used to track the portion of time spent on async operations since local time is updated before the async wait and remote time is updated when async wait completes:

• kafka.network:type=RequestMetrics,name=LocalTimeMs,request=CreateAcls
• kafka.network:type=RequestMetrics,name=RemoteTimeMs,request=CreateAcls
• kafka.network:type=RequestMetrics,name=LocalTimeMs,request=DeleteAcls
• kafka.network:type=RequestMetrics,name=RemoteTimeMs,request=DeleteAcls

Deprecate existing Scala Authorizer Trait

kafka.security.auth.Authorizer will be deprecated along with all the supporting Scala classes including Resource, Operations and ResourceTypes. A new AuthorizerWrapper class will be introduced to wrap implementations using the Scala trait into the new Java interface. All usage of Authorizer (e.g. in KafkaApis) will be replaced with the new authorizer interface.

AclAuthorizer

A new authorizer implementation will be added. kafka.security.authorizer.AclAuthorizer will implement the new interface, making use of the additional request context available to improve authorization logging. This authorizer will be compatible with SimpleAclAuthorizer and will support all its existing configs including super.users.

SimpleAclAuthorizer

SimpleAclAuthorizer will be deprecated, but we will continue to support this implementation using the old API. Since it is part of the public API, all its public methods will be retained without change. This enables existing custom implementations that rely on this class to continue to be used.

Optional Interfaces

Reconfigurable

kafka.server.DynamicBrokerConfig will be updated to support dynamic update of authorizers which implement org.apache.kafka.common.Reconfigurable. Authorizer implementations can react to dynamic updates of any of its configs including custom configs, avoiding broker restarts to update configs.

Compatibility, Deprecation, and Migration Plan

What impact (if any) will there be on existing users?

Existing authorizer interfaces and classes are being deprecated, but not removed. We will continue to support the same config with the old API to ensure that existing users are not impacted.

If we are changing behavior how will we phase out the older behavior?

We are deprecating the existing Scala authorizer API. These will be removed in a future release, but will continue to be supported for backward compatibility until then. Until the old authorizer is removed, no config changes are required during upgrade.

Test Plan

All the existing integration and system tests will be updated to use the new config and the new authorization class. Unit tests will be added for testing the new methods and parameters being introduced in this KIP. An additional integration test will be added to test authorizers using the old Scala API.  

Rejected Alternatives

Description of Authorizer as proposed in KIP-50

KIP-50 proposes to return a textual description of the authorizer that can be used in tools like AclCommand. Since we don’t support returning a description using AdminClient and none of the other pluggable APIs have similar support, this KIP does not add a method to return authorizer description.

Separate authorizers for each listener

In some environments, authorization decisions may be dependent on the security protocol used by the client or the listener on which the request was received. We have listener prefixed configs to enable independent listener-specific configs for authentication etc. But since authorizers tend to cache a lot of metadata and need to watch for changes in metadata, a single shared instance works better for authorization. This KIP proposes a single authorizer that can use listener and security protocol provided in the authorization context to include listener-specific authorization logic.

Extend SimpleAclAuthorizer to support the new API

SimpleAclAuthorizer is part of our public API since it is in the public package kafka.security.auth. So we need to ensure that the old API is used with this authorizer if custom implementations extend this class and override specific methods. So this KIP deprecates, but retains this implementation and adds a separate implementation that uses the new API.

Make authorize() asynchronous

Authorize operations in the existing Authorizer are synchronous and this KIP proposes to continue to authorize synchronously on the request thread while processing each request. This requires all ACLs to be cached in every broker to avoid blocking request threads during authorization. To improve scalability in future, we may want to support asynchronous authorize operations that may perform remote communication, for example with an LRU cache. But asynchronous authorize operations add complexity to the Kafka implementation. Even though we may be able to use the existing purgatory, additional design work is required to figure out how this can be implemented efficiently.  So it was decided that we should keep the authorization API synchronous for now. In future, we can add async authorize as a new method on the API if requiredIn some environments, authorization decisions may be dependent on the security protocol used by the client or the listener on which the request was received. We have listener prefixed configs to enable independent listener-specific configs for authentication etc. But since authorizers tend to cache a lot of metadata and need to watch for changes in metadata, a single shared instance works better for authorization. This KIP proposes a single authorizer that can use listener and security protocol provided in the authorization context to include listener-specific authorization logic.