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"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."

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

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

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

Public Interfaces

we We extend the "sasl.kerberos.principal.to.local.rules"  format This is done by adding a  format by supporting  "/L" to (toLowerCase) at 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.

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