Store secret environment variables

[JorritSalverda]

In order to push containers to registries, deploy containers to any environment, etc a secret is usually required.

To benefit from version controlling the secrets it would be nice to store them encrypted in plain sight in the manifest, but storing them in a database could be an easier alternative.

[JorritSalverda]

Encrypted secrets can be added to the .estafette.yaml manifest. They're encrypted using AES-256 encryption and then base64 url encoded. The nonce is prefixing the string and separated with a dot, similar to how bcrypt adds the salt. The entire string is then wrapped in estafette.secret(<nonce>.<encrypted string>) and can be used for any environment variable, like this:

    env:
      DOCKER_HUB_USERNAME: estafette.secret(...)

Generating the encrypted string can be done via Slack integration with Slash command /estafette encrypt <unencrypted secret string>.