Subscribe to Twitch EventSub webhook events for live stream and channel point redemption notifications

Steps

1. Obtain an app access token using the client credentials OAuth flow with the required scopes for the subscription types needed (e.g., channel:read:redemptions for channel point events)
2. Register a publicly reachable HTTPS webhook callback URL that can respond to Twitch's challenge verification request with a 200 OK and the echoed challenge string
3. Call the EventSub subscriptions endpoint (POST to the subscriptions resource) with the subscription type, version, condition (e.g., broadcaster_user_id), and transport object specifying method 'webhook' and the callback URL
4. Twitch sends a verification challenge POST to the callback URL; respond within the required time window by returning the challenge value to confirm the subscription
5. On receiving event notifications, verify the Twitch-Message-Signature header using the HMAC of the message ID, timestamp, and raw body with the subscription's secret to reject forged requests
6. Handle duplicate deliveries by checking the Twitch-Message-Id header and deduplicating against recently processed IDs