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Current state: Accepted

Discussion thread: here 

JIRA: KAFKA-5764 - Getting issue details... STATUS

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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 to a customized rule in The format of 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."

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

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

However, this may not be desired given how different operating system handle usernames, where 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, the rule can support to force the translated result to be all lower case.

Proposed Changes

We propose to extend ""  config rule format/syntax by supporting an optional  "/L" (toLowerCase) at the end of the rule. Since usernames are locale insensitive strings, we propose to use Locale.ENGLISH for the case conversion

 For example, given the rules

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

However, it must be noted that this does not affect how pattern matches on input and therefore that will still be case-sensitive.

Compatibility, Deprecation, and Migration Plan

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