How to get GitLab CI variables into the Sinatra app to query Google Cloud Datastore? - ruby

Question

Short:
I want to be able to deploy a Sinatra app without hardcoded secrets and variables using Google Cloud App Engine. Deploying to App Engine while ensuring the environment variables get loaded from the Google Cloud Datastore was the suggested option. I hoped to find something similar to the simplicity of Heroku, but this is not the case.
Question:
How would I get the $SERVICE_ACCOUNT environment information (that I've set in the GitLab CI / CD section) as the credentials value in foobar.rb?
app.yaml:
image: google/cloud-sdk:latest
before_script:
- apt-get install -y ruby-full build-essential
- gem install bundler
- bundle config --global silence_root_warning 1
- bundle install
after_script:
- rm /tmp/$CI_PIPELINE_ID.json
deploy_production:
stage: deploy
environment: Production
only:
- production
script:
- echo $SERVICE_ACCOUNT > /tmp/$CI_PIPELINE_ID.json
- gcloud auth activate-service-account --key-file /tmp/$CI_PIPELINE_ID.json
- gcloud --quiet --project $PROJECT_ID app deploy app.yaml
foobar.rb:
...
require "google/cloud/datastore"
class App < Sinatra::Application
if settings.production?
data_store = Google::Cloud::Datastore.new(
project: 'foobar',
credentials: "???"
)
query = data_store.query "kindoffoobar"
results = data_store.run query
# Set each result as an env variable
results[0].properties.to_h.each do |key, value|
ENV[key]= value
end
end
... rest of app