Status

Current state: Draft

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

JIRA: here [Change the link from KAFKA-1 to your own ticket]

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

Motivation

With the adoption of JEP 411: Deprecate the SecurityManager for Removal in Java 17, the SecurityManager is now deprecated, and will be removed in an unknown future version.

As Kafka supports multiple versions of Java (8, 11, 17, 21 for 3.x, 11, 17, 21 for 4.x), we should decide how to handle this deprecation and removal, and what replacements or mitigations we can provide for users of Kafka.

Kafka has a compile-time dependency on the AccessController  class in clients , core , and connect:runtime , and the removal of SecurityManager and it's accompanying classes would make these modules un-buildable with their current implementation.

Public Interfaces

The Kafka project should to define a major release in which SecurityManager support will be removed. It is not possible to remove support for this feature in a minor release, as it would constitute a breaking change.

There are two strategies for approaching the removal that we should pursue concurrently:

Remove SecurityManager support as soon as possible

As SecurityManager has not yet been removed from Java, we have the opportunity to remove it ourselves first.

For example, if SecurityManager is removed from the Kafka codebase in 4.0, and SecurityManager is removed from Java 25, users of Kafka 4.x can immediately upgrade to Java 25 without special considerations.

However, there are some problems with removing support quickly:

1. Java 11 still has the non-deprecated SecurityManager, and Kafka 4.0 must support Java 11. If we were to remove SecurityManager support from Kafka 4.0, users on Java 11 would experience a removal without a prior deprecation.
2. Java 17 does not have the replacement Subject API https://bugs.openjdk.org/browse/JDK-8267108 , and Kafka 4.0 must support Java 17. We would need dual support for the old and new APIs.

The earliest we could remove the SecurityManager without tech-debt is when Java 21 could become the minimum supported Java version. This is not planned for Kafka currently, but would probably be Kafka >=6.0.

Remove compile-time usages & detect SecurityManager removal at runtime

The longer it takes for Kafka to remove SecurityManager support, the more likely that the Java removal will take place before Kafka's removal is complete. To be prepared, we should anticipate that the project will need to support both versions with and without SecurityManager, using the same codebase & artifacts.

This can be done by replacing direct references to deprecated APIs with reflection, and gracefully changing the behavior for Java versions without the SecurityManager. When Java 21 becomes the minimum supported Java version, the reflective implementations could be removed and replaced with direct calls to the modern API.

Proposed Changes

The SaslClientCallbackHandler and OAuthBearerSaslClientCallbackHandler in clients  will no longer call Subject.getSubject , and instead will use the JDK 18+ Subject.current API: https://bugs.openjdk.org/browse/JDK-8267108 .
The SaslClientAuthenticator and SaslServerAuthenticator in clients will use the Java 18+ Subject.callAs API rather than the deprecated Subject.doAs function. This has a backwards-compatible implementation that will presumably be replaced when SecurityManager is removed.
The calls to getSubject, current, doAs, and callAs will be replaced with reflection. If Java 18 is available, the new functions will be used. Otherwise, the legacy API will be called.

The calls to AccessController.doPriviliged  in core  and connect:runtime: used for ClassLoader instantiation will be replaced with reflection. If the doPriviliged call is not available, the privileged operations will be done in the original context.

Compatibility, Deprecation, and Migration Plan

Users upgrading to a version of Java or Kafka without SecurityManager support will need to disable their security manager implementations/configurations.

Users upgrading to Java 17+ (in which SecurityManager was deprecated) already receive a warning message on startup.

Test Plan

There are currently no tests exercising the SecurityManager interface in Kafka, and no new tests for the end-to-end behavior will be added for this project.

Further tests will compare the reflective implementations to the old and new APIs. This is to ensure that changing the legacy APIs to reflection, and that later when the reflection is replaced with the new APIs, the behavior will stay the same throughout. These tests can mock the AccessController and Subject classes to make it appear that the removal has taken place.

Rejected Alternatives

Wait until SecurityManager is removed to change the implementations (do nothing)

When the first Java version without SecurityManager is released, there will have already been a number of Kafka minor and patch releases made. All of these will be unable to run with the new Java version, regardless of if the user was using the SecurityManager at all. This also includes users of the clients, who will be unable to run in the latest Java version until the clients have been released again.

Similarly, developers will be unable to build older branches of Kafka with the new Java version, and this will be generally inconvenient. When we front-load the effort in this migration, we can ensure that when the removal takes place, the most recent Kafka releases are already compatible.

Since removing SecurityManager is a breaking change, we would have to either delay support for the new Java version significantly, or perform a major release of Kafka when we might not be prepared for it. These negatives outweigh the maintenance burden of making these function calls reflective.

Set a removal date for Java 11 / Java 17 support

This should be delegated to another KIP with a dedicated discussion. This KIP can be blocked on that one, or be conditional. For example, we can agree here that in the major release which removes Java 17 support, we will also remove SecurityManager support, but not specify when the removal of Java 17 support will take place.

Implement a alternative to the SecurityManager for use with Kafka

The SecurityManager is a flawed design, and we should not replicate it or try to solve those problems in a similar way. Instead should encourage users to use the process boundary as a security boundary.