# Get currently logged-in customer ID

Returns the customer ID of the currently authenticated customer from their Shopify session. This endpoint is used by the customer portal UI to identify which customer is logged in.

Use Cases:
- Customer portal initialization - determine who's logged in
- Fetch customer-specific data (subscriptions, orders, settings)
- Validate customer session before displaying sensitive information
- Personalize customer portal UI with customer name/email

How it works:
- Customer must be logged in to their Shopify customer account
- Session is validated via Shopify App Proxy
- Returns Shopify customer ID (numeric)

Important Notes:
- This endpoint only works when called from the shop domain (via Shopify App Proxy)
- Customer must be logged in to Shopify
- Returns null if customer is not authenticated
- Do not use this for external API integrations - use External APIs with explicit customer ID instead

Authentication: Requires active Shopify customer session (browser-based)

Endpoint: GET /subscriptions/cp/api/logged-in-customer
Version: 0.0.1