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From Kafka documentation 

"By default, the SASL user name will be the primary part of the Kerberos principal. One can change that by
setting sasl.kerberos.principal.to.local.rules to a customized rule in server.properties. The format of
sasl.kerberos.principal.to.local.rules is a list where each rule works in the same way as
the auth_to_local in Kerberos configuration file (krb5.conf)  

Each rules starts with RULE: and contains an expression in the format [n:string](regexp)s/pattern/replacement/g."

Public Interfaces

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

A public interface is any change to the following:

• Binary log format

• The network protocol and api behavior

• Any class in the public packages under clientsConfiguration, especially client configuration

  • org/apache/kafka/common/serialization

  • org/apache/kafka/common

  • org/apache/kafka/common/errors

  • org/apache/kafka/clients/producer

  • org/apache/kafka/clients/consumer (eventually, once stable)

• Monitoring

• Command line tools and arguments

• Anything else that will likely break existing users in some way when they upgrade

Proposed Changes

Currently, translations based on rules are done maintaining the case of the input principal. For example, given the rule

RULE:[1:$1@$0](.*@EXAMPLE.COM)s/@.*//

If the source string is joe-qa@EXAMPLE.COM, the result is joe-qa
If the source string is JOE-QA@EXAMPLE.COM, the result is JOE-QA
If the source string is Joe-QA@EXAMPLE.COM, the result is Joe-QA

However, this may not be desired given how different operating system handle usernames, where as some are case-sensitive
and some are case-insensitive. For example, Linux is case-sensitive and Windows is case-insensitive.

To help with this issue, rule should support to force the translated result to be all lower case.

ReferenceDescribe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.

1. https://community.hortonworks.com/articles/14463/auth-to-local-rules-syntax.html

Public Interfaces

we extend the "sasl.kerberos.principal.to.local.rules"  format This is done by adding a "/L" to the end of the rule. However, it must be noted that this does not affect how pattern matches on input and therefore that will still be case-sensitive.

RULE:[1:$1@$0](joe-qa-.*@EXAMPLE.COM)s/.*/JOE-QA//L
RULE:[1:$1@$0](JOE-QA-.*@EXAMPLE.COM)s/.*/JOE-QA-UPPER//L
RULE:[1:$1@$0](.*@EXAMPLE.COM)s/@.*///L

If the source string is joe-qa-cl1@EXAMPLE.COM, the result is joe-qa
If the source string is JOE-QA-cl1@EXAMPLE.COM, the result is joe-qa-upper
If the source string is joe_user@EXAMPLE.COM, the result is joe_user
If the source string is JOE_USER@EXAMPLE.COM, the result is joe_user

Proposed Changes

Compatibility, Deprecation, and Migration Plan

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