Merge rails secrets with ENV

application.rb

module CredentialsDemo
  class Application < Rails::Application
    creds = credentials[Rails.env.to_sym]
              .with_indifferent_access
              .transform_keys(&:upcase)
              .transform_values(&:to_s)
    ENV.merge! creds.merge(ENV)
  end
end

# usage:
# ENV['MY_SECRET']