Subscribe to Twitch EventSub events via WebSocket transport for real-time in-game notifications

Steps

1. Obtain a user access token with the required scopes for your desired event types (e.g., channel.follow requires moderator:read:followers scope) using the OAuth authorization code flow.
2. Connect to the Twitch EventSub WebSocket endpoint; immediately after connection, receive a session_welcome message containing a session_id.
3. Create a subscription by calling the EventSub Subscriptions API (POST to the subscriptions endpoint) with the event type, version, condition (e.g., broadcaster_user_id), transport type of websocket, and the session_id from the welcome message.
4. Listen for notification messages on the WebSocket; each message contains a subscription object and an event payload specific to the subscribed event type.
5. Respond to keepalive messages within the keepalive_timeout_seconds value specified in the welcome message; if no message arrives within that window, the connection is considered dead and must be re-established.
6. Handle reconnect messages by connecting to the provided reconnect_url before closing the old connection, then migrate subscriptions to the new session.