Use case with KMS

[MrAtheist]

Tell us about the issue

Lack of documentation around kms

Description:
I have wired up rds logs --> kinesis via database activity stream, which is then streamed to elk via a "logstash pipeline". One tiny problem here is that the rds logs are all just a giant blob of mess getting spammed to elk.
There seems to be this plugin (looks to be deprecated...) that deals with kms. Are there any documentation within this repo around integration specifically with kms?

cipher {
    algorithm => "aes-128-cbc"
    cipher_padding => 1

    iv_random_length => 16
    key => "WHATS_IN_HERE?"   <----
    key_size => 16

    mode => "decrypt"
    source => "message"
    target => "message"
    base64 => true
}  

Anything else?