use CI=true parameter to detect that the build is happening on GitHub Action platform

[developer-guy]

The GitHub Actions runner now sets the CI=true environment variable by default.
Source: https://github.blog/changelog/2020-04-15-github-actions-sets-the-ci-environment-variable-to-true/

Wouldn't be nice if we can check this environment variable that I mentioned in the title of the issue to detect the build is actually happening in GitHub Action as an additional control to this code here.

WDYT? @laurentsimon, btw, I'm willing to do this if you agree with the idea, thanks.

[laurentsimon]

Hey

First, thanks for the interest. Shameless plug, we have released a v1 for the Go builder (more coming up soon) in github.com/slsa-framework/slsa-github-generator (official announcement very soon).

(We have not migrated the ko builder yet :/)

re: the CI variable. Can you tell me more about detect the build is actually happening in GitHub Action? The signature for the provenance is done via certificate provided by Fulcio, and has the identity of the builder/GitHub in it, so we're certain the build was made on a GitHub Action.

May I suggest you create an issue on github.com/slsa-framework/slsa-github-generator? That will generate more discussion than this repo :-)

Thank you!