OPA Google Calendar Integration

Companion code for the Styra blog on integrating OPA with the Google Calendar API as a datasource.

Extract events from Google Calendar

Create a GCP service account. You do not need to change any defaults.
In your service account settings, click "Keys" and "New key". Download the credentials file.
Export the service account email as an env variable: export SERVICE_ACCOUNT=opa-calendar@opa-lab.iam.gserviceaccount.com
Export the private key as an env variable: export SIGNING_KEY=$(cat credentials.json | jq -r .private_key)
In Google Calendar, click the calendar you want to use and choose "Settings and sharing".
From the menu to the left, click "Share with specific people". Add the service account e-mail address.
From the menu to the left, click "Integrate calendar". Copy the Calendar ID value.
Export the calendar ID: export CALENDAR_ID=<calendar ID>
Extract events and save to file: opa eval --format raw --data events.rego data.google.calendar > calendar.json