Keep unveiled credentials in Elasticsearch (using jdbc-river) - ruby-on-rails

Question

I use the jdbc-river to fill my Elasticsearch instance from a PostgreSQL database. The river's record is created with the following ruby's code (since I query ES from a Rails app):
require 'elasticsearch'
client = Elasticsearch::Client.new
client.create :index => "_river", :type => "ldi", :id => "_meta", :body =>
{
:type => :jdbc,
:jdbc => {
:driver => "org.postgresql.Driver",
:url => "jdbc:postgresql://localhost:5432/" + ENV['DB_NAME'],
:user => ENV['DB_USER'],
:password => ENV['DB_PASS'],
:index => ENV['DB_NAME'],
:type => "ldi",
:sql => "select id as _id, * from ldis"
}
}
I'm using envirnoment variables for the database credentials to avoid showing the actual ones. The problem is that once the record is added to ES, actual credentials are unveiled. Thus, you can query ES and obtain something like this:
"hits": {
"total": 6,
"max_score": 1,
"hits": [
{
"_index": "_river",
"_type": "ldi",
"_id": "_meta",
"_score": 1,
"_source": {
"type": "jdbc",
"jdbc": {
"driver": "org.postgresql.Driver",
"url": "jdbc:postgresql://localhost:5432/any_dbname",
"user": "any_dbuser",
"password": "any_dbpass",
"index": "any_index",
"type": "ldi",
"sql": "select id as _id, * from ldis"
}
}
}
....
Is there any way to keep them in secret?