Status

Current state:  [One of "Under Discussion", "Accepted", "Rejected"]Closed (Covered by KIP-189)

Discussion thread: here (Original Archive) (Markmail)

JIRA: KAFKA-4454

Released: <Kafka Version>

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

Motivation

Kafka allows users to plugin a custom PrincipalBuilder and a custom Authorizer by specifying the classpath of the corresponding classes in the config.

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This issue can be addressed if Kafka stores preserves the original Principal object when it processes the incoming request, before handing it over to the API threads. The Authorizer will then be able to access this Principal object and use it to verify the ACLs.

New or Changed Public Interfaces

This KIP introduces a new constructor in the KafkaPrincipal class, that takes in an additional parameter of type Java Principal. It also introduces a new API in PrincipalBuilder, that would build a Java Principal from the passed in map of configs. kafka-acls.sh would take in 2 optional command line parameters specifying the PrincipalBuilder class name and the properties used to create the PrincpalBuilder.

Beyond the proposed new configuration key this KIP makes no changes to client or server public APIs.

Proposed Changes

change to Session class to accept a parameter of Java Principal type  instead of KafkaPrincipal type.

This change will not affect the default ACL Authorizer (SimpleAclAuthorizer) as we would generate a KafkaPrincipal from the Java Principal in the default Authorizer.

Proposed Changes

• Change the Session class to accept a parameter of type Java Principal instead of KafkaPrincipal.

• Add a new field to KafkaPrincipal called "channelPrincipal" of type java.security.Principal. 

• Add a new constructor to KafkaPrincipal that takes in an additional parameter of type java.security.Principal as follows :

  Code Block
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  publiccase class KafkaPrincipal implements Principal { ... private Principal channelPrincipal; // New Constructor public KafkaPrincipal(String principalType, String name, Principal channelPrincipal) { if (principalType == null || name == null) { throw new IllegalArgumentException("principalType and name can not be null"); } this.principalType = principalType; this.name = name; this.channelPrincipal = channelPrincipal; } public KafkaPrincipal(String principalType, String name) { this(principalType, name, null); } ... public Principal getChannelPrincipal() { return this.channelPrincipal; } }Session(principal: Principal, clientAddress: InetAddress)

• The Authorizer can access this principal object as follows :

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  public boolean authorize(RequestChannel.Session session, Operation operation, Resource resource) { ... KafkaPrincipalPrincipal principal = session.principal(); // User_Defined_Principal should implement java.security.Principal User_Defined_Principal principal = (User_Defined_Principal) principal.getChannelPrincipal(); ... }

• Changes to kafka-acls.sh

• Kafka-acls.sh will allow to specify a custom PrincipalBuilder class using a new command line parameter "-- principalBuilder" and PrincipalBuilder configs using a new command line parameter "--principalBuilder-properties".

• The "--allow-principal" will take list of properties as follows :

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  bin/kafka-acls.sh ...... --principalBuilder <PrincipalBuilder-class> --principalBuilder-properties <PrincipalBuilder-properties> --add --allow-principal <principal-properties> --allow-principal <principal-properties> ...... --operations Read,Write --topic Test-topic

• Add a new API to PrincipalBuilder :

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  public interface PrincipalBuilder extends Configurable { ... /** * Build a Principal using the provided configs. * * @param principalConfigs configs used to create the Principal * @return Principal */ Principal buildPrincipal(Map<String, ?> principalConfigs); ... }

• The specified PrincipalBuilder class will be responsible for building the Principal using the <principal-properties>.
• The Principal generated by this PrincipalBuilder can then be included in KafkaPrincipal using the new constructor specified above.
The "--principalBuilder" and "--principalBuilder-properties" parameters are optional. If its not specified, the Kafka-acls.sh would still work as it does today

User_Defined_Principal is the Principal generated by the PrincipalBuilder and it implements Java Principal.

Compatibility, Deprecation, and Migration Plan

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

There is no compatibility impact as there is no change in behaviorThis KIP is a pure addition to existing functionality and does not include any backward incompatible changes.

Test Plan

- Unit tests to validate that new changes work as expected without affecting the existing behavior.

Rejected Alternatives

Alternative 1 :

• Kafka-acls.sh will allow to specify a custom PrincipalBuilder using a new command line parameter "-- principalBuilder" and PrincipalBuilder configs using a new command line parameter "--principalBuilder-properties". Users can use these to build their custom Principal (that implements Java Principal). Add a new API to PrincipalBuilder Interface :

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  public interface PrincipalBuilder extends Configurable { ... /** * Build a Principal using name. * * @param name Principal name * @return Principal */ Principal buildPrincipal(String name); ... }

• This PrincipalBuilder API will then be used to generate a Principal using the names specified in --allow-principal and --deny-principal parameters. This Principal can be included in KafkaPrincipal using the new constructor specified above.
• This alternative was rejected due to following reasons :

  1. Since the Principal is built using the "--principalBuilder-properties", users can only specify a particular type of Principal(s) (using --allow-principal / --deny-principal) at a time.

  2. If users want to specify multiple types of Principals, they will have to run the kafka-acls.sh multiple times with different "--principalBuilder-properties", even if the Principals might have the same name. For example, we can have a service Principal with name "XYZ" and a user Principal with name "XYZ".

• Due to above reasons, it is quite clear that it is less user friendly and not intuitive.

Alternative 2 :

• Changes to kafka-acls.sh

  • Kafka-acls.sh will allow to specify a custom PrincipalBuilder class using a new command line parameter "-- principalBuilder" and PrincipalBuilder configs using a new command line parameter "--principalBuilder-properties".

  • The "--allow-principal" will take list of properties as follows :

    Code Block
    language java theme Midnight
    bin/kafka-acls.sh ...... --principalBuilder <PrincipalBuilder-class> --principalBuilder-properties <PrincipalBuilder-properties> --add --allow-principal <principal-properties> --allow-principal <principal-properties> ...... --operations Read,Write --topic Test-topic

  • Add a new API to PrincipalBuilder :

    Code Block
    language java theme Midnight
    public interface PrincipalBuilder extends Configurable { ... /** * Build a Principal using the provided configs. * * @param principalConfigs configs used to create the Principal * @return Principal */ Principal buildPrincipal(Map<String, ?> principalConfigs); ... }

  • The specified PrincipalBuilder class will be responsible for building the Principal using the <principal-properties>.
  • The Principal generated by this PrincipalBuilder can then be included in KafkaPrincipal using the new constructor specified above.

  • The "--principalBuilder" and "--principalBuilder-properties" parameters are optional. If its not specified, the Kafka-acls.sh would still work as it does today.

• This was rejected as per discussions on the email thread as this is a nice to have feature but there is no urgent need for this.