Certificates in build environment

[Petr Buchyn]

I want to create a Kubernetes deploy by Bitbucket Pipelines.
I've read this tutorial:
https://confluence.atlassian.com/bitbucket/deploy-to-kubernetes-892623297.html

This tutorial is clear, except one point: how do I get ca.crt in my build environment?
I can pass environment variables to build, but how do I pass files (certificates etc.) to build environment?