Shop Pay client_id request - CartBridge agentic cart layer for Shopify merchants

[morewillie]

Hi UCP / Shopify team,

We'd like to request access to delegated Shop Pay agent credentials for CartBridge.

Product

CartBridge is a merchant-installed Shopify app and agentic cart adapter:

• Public site: https://cartbridge.ai
• UCP agent profile: https://cartbridge.ai/.well-known/ucp-agent-profile.json
• Agent instructions: https://cartbridge.ai/llms.txt
• MCP runtime setup: https://cartbridge.ai/agent-runtime-setup.md
• OpenAPI: https://cartbridge.ai/openapi.yaml

The goal is to let a buyer ask an LLM to find a product from a Shopify merchant, approve an exact quote, and complete the purchase from the agent surface without CartBridge ever collecting or storing card data.

Current implementation

CartBridge already supports:

• Shopify OAuth install for merchants.
• Native Shopify Storefront cart creation.
• Signed, expiring quote ledger.
• Merchant policy enforcement: approval required, max total, blocked product types.
• Native Shopify checkout URL handoff.
• Order/payment/fulfillment/refund webhook reconciliation.
• LLM-facing purchase result endpoint after checkout/order sync.
• MCP tools for LLM runtimes:
  • cartbridge_search_products
  • cartbridge_prepare_checkout
  • cartbridge_create_cart
  • cartbridge_approve_checkout
  • cartbridge_purchase_result
  • cartbridge_ucp_checkout
  • cartbridge_wait_for_order

Live production smoke against our Shopify test store succeeds through native checkout handoff:

• Store: cb-test-store-x5l812hm.myshopify.com
• Product selected: Selling Plans Ski Wax
• CartBridge creates a native Shopify cart and signed quote.
• CartBridge returns a native Shopify checkout URL.
• purchaseResult.state returns checkout_started and then waits for Shopify order webhook sync.

What we're requesting

We need access for the next step:

1. Shopify agent credentials for authenticated Checkout MCP calls, if separate from the Dev Dashboard Catalog credential flow.
2. A delegated Shop Pay client_id that supports Shop Token generation for buyer-authorized payment.
3. Any required allowlisting or test surface needed to call merchant UCP endpoints without storefront password redirects.

Intended delegated Shop Pay flow

We want to implement the flow described in the Shop Pay handler spec:

1. Discover dev.shopify.shop_pay from the merchant checkout/payment handler config.
2. Initialize delegated Shop Pay payment using the merchant shop_id and CartBridge client_id.
3. Present the Shop Pay authorization surface to the buyer from the LLM/app surface.
4. Receive a checkout-scoped, single-use Shop Token.
5. Submit that token through Checkout MCP complete_checkout after explicit buyer approval.
6. Return final order confirmation to the LLM via CartBridge purchaseResult.

We will not collect, proxy, log, or store raw card data. Shopify remains merchant of record and payment processor.

Security / buyer authority model

CartBridge requires:

• Agent authentication.
• Merchant install and allowlisting.
• Buyer IP on server-side Storefront calls.
• Explicit user authority on cart creation.
• Quote approval before checkout handoff or completion.
• Idempotency keys for completion operations.
• Audit records for original user request, agent intent, quote, approval, checkout handoff/completion attempt, and Shopify order webhook.

V1 blocks gift cards, cash equivalents, subscriptions/selling plans, and over-policy totals unless explicitly allowed by merchant policy.

Current blocker

Our Checkout MCP probe is implemented, but the current test store UCP endpoint redirects to /password:

{
  "ok": false,
  "status": 302,
  "location": "https://cb-test-store-x5l812hm.myshopify.com/password"
}

Native CartBridge checkout handoff works. The remaining blocker is access to the authenticated/delegated path needed for in-agent Shop Pay completion.

Contact

CartBridge: https://cartbridge.ai
Support/contact: support@cartbridge.ai
GitHub account posting this request: @morewillie

Happy to provide demo credentials, a live walkthrough, or any additional compliance/security detail needed for access.