I don't understand the significance of the  (?<!\\\\) assertion in the regex in the OP (copied as-is in tybalt89's reply). It suppresses elision of secret values when the single- or double-quoted key phrase is immediately preceded by a  \\ double backslash but not by a single backslash. Is this intended? Output from tybalt89's working code with a few minor output formatting modifications:

c:\@Work\Perl\monks\1nickt>perl tybalt89_pm1206554_1.pl
{'password' => 'secret'} -> {'password' => '***'}
{"password" => "sec\"ret"} -> {"password" => "***"}
{\'password' => 'secret'} -> {\'password' => '***'}
{\"password" => "sec\"ret"} -> {\"password" => "***"}
{\\'password' => 'secret'} -> {\\'password' => 'secret'}
{\\"password" => "sec\"ret"} -> {\\"password" => "sec\"ret"}
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