The API uses API keys to authenticate requests. You can view and manage your API keys in your settings page under the security tab in
API Keys are under Settings > Security
Test mode secret keys have the prefix cal_test_ and live mode secret keys have the prefix cal_live_.
Your API keys carry many privileges, so be sure to keep them secure! Do not share your secret API keys in publicly accessible areas such as GitHub, client-side code, and so forth.
Authentication to the API is performed via URL Query Params. Provide your API key as a query param like:
All API requests must be made over HTTPS. Calls made over plain HTTP will fail. API requests without authentication will also fail.