package kafka.security.auth

import kafka.network.RequestChannel.Session
import kafka.server.KafkaConfig

/**
 * Top level interface that all plugable authorizer must implement. Kafka server will read "authorizer.class" config
 * value at startup time, create an instance of the specified class and call initialize method.
 * authorizer.class must be a class that implements this interface.
 * If authorizer.class has no value specified no authorization will be performed.
 *
 * From that point onwards, every client request will first be routed to authorize method and the request will only be
 * authorized if the method returns true.
 */
trait Authorizer {
  /**
   * Guaranteed to be called before any authorize call is made.
   */
  def initialize(kafkaConfig: KafkaConfig): Unit
  
  /**
   * @param session The session being authenticated.
   * @param operation Type of operation client is trying to perform on resource.
   * @param resource Resource the client is trying to access.
   * @return
   */
  def authorize(session: Session, operation: Operation, resource: Resource): Boolean

  /**
   * add the acls to resource, this is an additive operation so existing acls will not be overwritten, instead these new
   * acls will be added to existing acls.
   * @param acls set of acls to add to existing acls
   * @param resource the resource to which these acls should be attached.
   */
  def addAcls(acls: Set[Acl], resource: Resource): Unit

  /**
   * remove these acls from the resource.
   * @param acls set of acls to be removed.
   * @param resource resource from which the acls should be removed.
   * @return true if some acl got removed, false if no acl was removed.
   */
  def removeAcls(acls: Set[Acl], resource: Resource): Boolean

  /**
   * remove a resource along with all of its acls from acl store.
   * @param resource
   * @return
   */
  def removeAcls(resource: Resource): Boolean

  /**
   * get set of acls for this resource
   * @param resource
   * @return empty set if no acls are found, otherwise the acls for the resource.
   */
  def getAcls(resource: Resource): Set[Acl]

  /**
   * get the acls for this principal.
   * @param principal
   * @return empty set if no acls exist for this principal, otherwise the acls for the principal.
   */
  def getAcls(principal: KafkaPrincipal): Set[Acl]
}

Session

This is session from https://reviews.apache.org/r/27204/.

object RequestChannel extends Logging {
	case class Session(principal: Principal, host: String)
}

KafkaPrincipal

/**
 * 
 * @param principalType type of principal. (i.e. for default implementation we will support user and group but custom authorizer can add more types.)
 * @param name name of the principal
 */
case class KafkaPrincipal(principalType: String, name: String) extends Principal 

ResourceType

package kafka.security.auth

/**
 * Types of resources.
 */
public enum ResourceType {
   CLUSTER,
   TOPIC,
   CONSUMER_GROUP
}

Resource

/**
 * @param resourceType type of Resource.
 * @param name name of the resource, for cluster this will always be "kafka-cluster", for topic it will be name of the topic, for group it will be group name.
 */
case class Resource(resourceType: ResourceType, name: String) 

Operation

package kafka.security.auth

/**
 * Different operations a client may perform on kafka resources.
 */
public enum Operation {
   READ, 
   WRITE,
   CREATE,
   DELETE,
   ALTER,
   DESCRIBE,
   CLUSTER_ACTION
}

In order to produce to a topic, the principal will require WRITE on the TOPIC. 

In order to consume from a topic using the new consumer API, the principal will need: READ on TOPIC and READ on CONSUMER-GROUP.

In order to edit topic config/add acls , the principal will require ALTER on the TOPIC.

PermissionType

public enum PermissionType { ALLOW, DENY }

AuthorizationException

/** 
 * Exception thrown when a principal is not authorized to perform an operation. 
 * @param message 
 */ 
class AuthorizationException(message: String) extends RuntimeException(message) { }

Acl

package kafka.security.auth 
/** 
 * An instance of this class will represent an acl that can express following statement. 
 * <pre> Principals P1,P2 has permissionType PT on Operations O1,O2 from hosts H1,H2. </pre> 
 * @param principals A value of user:* indicates all users. 
 * @param permissionType 
 * @param hosts A value of * indicates all hosts. 
 * @param operations A value of ALL indicates all operations. 
 */ 
case class Acl(val principals: Set[KafkaPrincipal], val permissionType: PermissionType, val hosts: Set[String], val operations: Set[Operation])

Default implementation

SimpleAclAuthorizer

• Out of the box implementation of the Authorizer.

• Self contained and no dependencies with any other vendor or providers.

• Will contain a ACLCache that will cache the broker acls and topic specific acls with a TTL of 1 hour.

• Deny will take precedence over Allow in competing acls. i.e. if 2 Acls are defined, one that allows an operation from all hosts and one that denies the operation from host1, the operation from host1 will be denied. 

• When no Acl is attached to a resource , this implementation will always fail close(deny all requests). 

• When any Acl is attached to a resource only users that are in the allowed list will have access. All users with no explicit allow acls will be denied access by default.

• Will allow principals that have READ or WRITE permission the DESCRIBE Operation as well without having to specify explicit acls.

• It will use zookeeper as the storage layer for acls. Acls will be stored in json format described below under /kafka-acls/resource-type/<resource-name>.

  SimpleAuthorizer

  authorize(session, operation, resource) { 
    principal = session.principal 
    remoteAddress = session.host 
   
    if(principal is one of the superuser) { 
      return true 
    } 
    acls = getAcl(resource) //will have a cache. 
    if(acls.isEmpty || acls.contains(allowAccessToEveryoneAcl)) 
      return true 
    
    if any deny acl's are configured for this principal/host/operation combination, deny the access. 
   
    otherwise check if any acl exist that explicitly allows operation for this principal/host/operation and return true if some acl is found. 
   
    no explicit allow acls were found so deny the access. 
  }

  Example Acl Json That will be stored in zookeeper

  {"version": 1, 
   "acls": [ 
  	{ 
        "principals": ["user:alice”, "group:kafka-devs"], 
  	  "permissionType": "ALLOW", 
        "operations": [ "READ", "WRITE" ], 
        "hosts": [ "host1", "host2" ] 
      }, 
     { 
       "principal": ["user:bob”, "user:*"] ,
       "permissionType": "ALLOW", 
       "operations": [ "READ" ], 
       "hosts": [ "*" ] 
     }, 
     { 
       "principal": "user:bob”, 
       "permissionType": "DENY", 
       "operations": [ "READ" ], 
       "hosts": [ "host1", "host2" ] 
     } 
   ] 
  }

Changes to existing classes

• KafkaServer will initialize the authorizer based on value of authorizer.class.name config. 

• KafkaAPI will have an additional field authorizer, which will be passed by KafkaServer at the time of server initialization. KafkaAPI will call authorizer.authorize for all requests that needs to be authorized.If the function returns false , KafkaApi will throw an AuthorizationException

• KafkaConfig will have 2 additional configurations. 
  I have considered zookeeper node ACLs as out of scope for this document, if we decide to make it part of this KIP we will have to change ZKUtils so it can set acls on all zkNodes. I already have an implementation for this (not tested yet ) however we will have to wait for KIP-4 to be merged.

  • authorizer.class.name: FQCN of the authroizer class to be used. Provided class must implement Authorizer interface.
  • kafka.superusers: list of users that will be given superuser access. These users will have access to everything. Users should set this to the user kafka broker processes are running as to avoid duplicate configuration for every single topic like ALLOW REPLICATION to BROKER_USER for TOPIC from ALL hosts.

  • authorizer.config.path: path to a properties file that will contain authorizer specific configuration. In case of DefaultAuthorizer implementation this config can contain the following 2 configs:

    • zookeeper.url: comma separated list of zookeeper host: port that default authorizer should use to store all the acls. Useful when the acl zookeeper store needs to be different from kafka zookeeper.

    • allow.everyone: The default authorizer implementation denies access to everyone and expects specific allow acls to be defined to grant access. If this flag is set to true it will allow access from everyone unless an explicit deny is found to revoke access.

Data Flows

Authentication and session initialization details are out of scope of this document. We will assume that the authentication is done before any authorization happens and the session instance is properly initialized. As mentioned above, we assume that on secure connection session has principal set to authenticated user and on non secure connections it is set to a special principal such that it's name() function returns "Anonymous".

Initialize Authorizer

Since this is pluggable architecture, users can easily replace the default provider implementation by writing their own custom provider and providing that class's FQCN as the value of config authorizer.class.name. On kafka server side on server initialization KafkaServer will read the value of authorizer.class.name, create an instance of the class name specified and call it's init method with KafkaConfig parameter. This instance will be passed as a constructor argument to KafkaAPI. 

If the value of authorizer.class.name is null, in secure mode the cluster will fail with ConfigException. In non secure mode in absence of config value for authorizer.class.name the server will allow all requests to all topics , even if the topic has configured acls. This is done purely for backwards compatibility and it will be a security hole. To avoid this we can always default to SimpleAclAuthorizer which will allow only access to topics that has acl configured to allow access for Anonymous users.

Acl Management (CLI)

Please see Kafka Authorization Command Line Interface