Encryption key for Docker deployment



I have Docker deployment of Concourse.
Trying to add Encryption of DB items, as written in https://concourse-ci.org/encryption.html
After adding the encryption, DB items are encrypted obviously.
So, Concourse instance needs some runtime key to use DB.
I see options to do it in Manifest through Bosh, but I don’t have Bosh (https://docs.pivotal.io/p-concourse/4-x/encryption.html).
Is there something like ENV variable for docker run / compose?

Thx in advance!