Where can I put Stripe for publishing and private keys?

I work in a development environment.

I have a stripe.rb file in / config / initializers whose contents are:

Rails.configuration.stripe = {
  :publishable_key => ENV['PUBLISHABLE_KEY'],
  :secret_key      => ENV['SECRET_KEY']
}

Stripe.api_key = Rails.configuration.stripe[:secret_key]

I tried to place them there (in ENV ['key-here']), but Stripe does not recognize them and returns an error.

To make it work, I pass them before starting my rails server:

PUBLISHABLE_KEY=pk_test_XXXXXXXXXXXXX SECRET_KEY=sk_test_XXXXXXXXXXXX rails s

Where to place these values ​​in a Rails application? (since I will start production soon)

thank