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However, this may not be desired given how different operating system handle usernames, whereas 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.

Reference

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

Proposed Changes

We propose to extend "sasl.kerberos.principal.to.local.rules"  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

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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

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

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