Change environment variables directly from Cloud Build

I know I can change the environment variables on Cloud Build using the web API, but that requires storing the user's API key somewhere in the project to authenticate. Is there any way to modify an environment variable when building from Cloud Build without requiring the API key?

Also, is there any way to retrieve the id of the current project and organization when building from Cloud Build? CloudProjectSettings.projectId and CloudProjectSettings.organizationId return empty/null values.