ACP Delegated Payment & SharedPaymentToken

Before writing code

Fetch live docs:

1. Fetch https://developers.openai.com/commerce/specs/payment/ for the delegated payment specification
2. Fetch https://docs.stripe.com/agentic-commerce/concepts/shared-payment-tokens for SPT implementation details
3. Web-search site:docs.stripe.com agentic-commerce delegate payment for Stripe integration guide
4. Web-search site:github.com agentic-commerce-protocol spec openapi delegate for the delegate payment OpenAPI spec

Conceptual Architecture

What Delegated Payment Solves

The agent facilitates purchases but must never see raw card data. Delegated payment creates a secure intermediary:

• Buyer's payment credentials go to the PSP (Stripe), not the agent or merchant
• PSP returns a single-use, scoped token (SPT)
• Agent passes the SPT to the merchant in the complete call
• Merchant charges via PSP using the SPT

End-to-End Flow

Buyer → Agent: "Buy this"
Agent → PSP: POST /agentic_commerce/delegate_payment (credentials + constraints)
PSP → Agent: SharedPaymentToken (single-use, scoped)
Agent → Merchant: POST /checkout_sessions/{id}/complete (with SPT)
Merchant → PSP: Charge using SPT
PSP → Merchant: Payment confirmation
Merchant → Agent: Session status = completed + order

SPT Constraints (Allowance)

Each SharedPaymentToken is scoped with:

• max_amount — Maximum chargeable amount (integer, minor units)
• currency — Currency code
• checkout_session_id — Tied to a specific session
• merchant_id — Only usable by the specified merchant
• expires_at — Expiration timestamp
• reason — Purpose of the allowance (value: "one_time" for single-use checkout tokens)

If any constraint is violated, the charge fails.

SPT Properties

• Single-use — Can only be charged once
• Time-bound — Expires after a configured duration
• Amount-scoped — Cannot exceed the max amount
• Merchant-scoped — Only the designated merchant can use it
• Session-scoped — Tied to a specific checkout session

3D Secure Flow

When the merchant returns authentication_required:

1. Agent receives a 3DS challenge
2. Agent performs 3DS authentication with the buyer
3. Agent calls complete again with authentication_result containing:
   • three_ds_cryptogram
   • electronic_commerce_indicator
   • transaction_id
   • version

SPT Webhook Events

PCI Considerations

• Direct /delegate_payment integration may affect PCI DSS scope
• Network tokens preferred over full PAN (FPAN) where possible
• Never log full card numbers or CVCs
• SPT itself is not PCI-sensitive — it's a vault reference

Best Practices

• Always set max_amount to the session total (not higher)
• Set short expiration times — just enough for the checkout completion
• Handle SPT expiration gracefully — re-provision if needed
• Implement SPT webhook listeners for lifecycle tracking
• Log SPT creation and usage for reconciliation (without sensitive data)

Fetch the delegated payment OpenAPI spec and Stripe SPT docs for exact endpoint, request/response schemas, and error codes before implementing.