ACP Client Skill

Execute checkout, cart, and order operations against the OpenLink Adaptive Commerce Platform (ACP) API using composable curl recipes. Triggered by natural-language purchase intents.

When to Use

• "I want to purchase {product}" / "Buy {product}" / "Get me a license for {product}"
• "Checkout {product}" / "Create a checkout for {offer-id}"
• "Update checkout {id}" / "Change quantity for checkout {id}"
• "Cancel checkout {id}" / "Cancel my order"
• "Complete checkout {id}" / "Pay for checkout {id}"
• "Add {product} to cart" / "Create a cart for {product}"
• "Get order {order-id}" / "Check status of order {order-id}"
• "Get a Stripe test token" / "Generate SPT for {amount}"
• "Use balance" / "Pay with balance"
• Any request referencing the ACP API, checkout sessions, carts, or OpenLink software license purchases.
• Accessing a paid/protected resource behind a 402 (MPP) paywall, when the authentication protocol (WebID-TLS/NetID-TLS, OAuth, Digest) or settlement route must be elicited. WebID-TLS/NetID-TLS always targets port 5443, never 443 — see the Auth Protocol Selection rule.

Prerequisites

• curl installed
• jq recommended (fallback awk JSON parsers provided)
• ACP_AUTH_TOKEN environment variable set, or user must obtain one manually
• STRIPE_API_KEY required for complete and spt flows

ACP Instances

Known ACP API endpoints. The default is shop.openlinksw.com; override via ACP_BASE_URL:

To use a non-default instance, set ACP_BASE_URL before invoking the skill:

export ACP_BASE_URL="https://ods-qa.openlinksw.com/acp"

Environment Variables

Intent-to-Flow Mapping

When the user expresses a natural-language intent, map it to the corresponding ACP flow:

Product Resolution

When the user names a product (e.g., "JDBC to ODBC bridge driver"), resolve it to an offer IRI using the catalog in references/product-catalog.md. Match against:

• schema:name
• skos:prefLabel
• skos:altLabel
• schema:description

If no match is found, ask the user for the full offer IRI or product URL.

Bearer Token Acquisition (Manual)

If ACP_AUTH_TOKEN is missing or invalid:

1. Prompt the user: "ACP bearer token not found. Please obtain one from the OAuth applications page."
2. Provide URLs:
   • Primary: https://ods-qa.openlinksw.com/oauth/applications.vsp
   • Alternative: https://shop.openlinksw.com/oauth/applications.vsp
   • Additional: any other Virtuoso instance the user specifies
3. Instructions:
   • Navigate to the URL
   • Log in via the authentication form (Digest, WebID-TLS, or social login)
   • Register a new OAuth application
   • Copy the generated bearer token
   • Export as ACP_AUTH_TOKEN or paste when prompted

Browser Automation

The skill uses Playwright (playwright-cli) for browser automation. PinchTab is a fallback if Playwright is unavailable.

Set the wrapper script path before use:

export PWCLI="{REPO_ROOT}/.opencode/skills/playwright/scripts/playwright_cli.sh"

Prerequisites

• npx (comes with Node.js/npm)
• Playwright browsers installed (first use): npx playwright install chromium

Workflow

1. Open page in headed mode: "$PWCLI" open <url> --headed
2. Snapshot for element refs: "$PWCLI" snapshot
3. Interact with elements by ref (e.g., "$PWCLI" click e79)
4. Capture screenshots or PDFs as needed

Subscription Payment Detection

After complete_checkout, the response may contain a links array with a subscription_payment entry. When present:

1. Extract the href value from the link with rel: "subscription_payment"
2. Open the link with Playwright:

   "$PWCLI" open <href> --headed
   "$PWCLI" snapshot

3. Present the snapshot to the user showing the payment form.
4. Ask the user if they want to proceed with payment.

Checkout Body Format

The create_checkout and update_checkout operations use items (not line_items) and capabilities as an empty object:

{
  "items": [
    { "id": "http://data.openlinksw.com/oplweb/offer/Offer-2020-10-virtuoso-8-app-developer-development-WKS-ANY#this", "quantity": 1 }
  ],
  "currency": "usd",
  "capabilities": {}
}

Output Format

• Default: Human-readable summary (checkout ID, order ID, status, total, receipt, subscription payment link if present)
• --json flag: Raw JSON from the API response, stable machine-readable output for agent consumption

Post-Purchase File Access Verification

After a checkout is completed and the subscription payment is processed, verify that the purchased file/resource is accessible:

1. Resolve the resource URL from the offer IRI — typically the offer's schema:subjectOf or the resource's canonical DAV/WebDAV path on the ACP instance.

2. Fetch with On-Behalf-Of delegation using the ACP bearer token:

   curl -sI -H "Authorization: Bearer ${ACP_AUTH_TOKEN}" \
     -H "On-Behalf-Of: {resource-iri}" \
     "{resource-url}"

   IMPORTANT: The On-Behalf-Of header value must be a bare WebID URI — no angle brackets. Correct: -H "On-Behalf-Of: https://example.com/path#fragment". Angle brackets cause delegation resolution failure (402/401). The {resource-iri} placeholder uses curly braces conventionally — the actual value is a bare IRI.

   • 200 OK → access granted, file is available
   • 401 Unauthorized → provisioning may be async; retry after a short delay
   • 403 Forbidden → access not granted; check order/subscription status
   • 404 Not Found → wrong resource URL; verify path
3. Report result to the user: confirmed accessible, or explain the issue.

MPP Purchase Flow for Protected Resources (Protocol-Agnostic)

Use this flow when accessing a paid resource behind a 402 Payment Required paywall (MPP) — e.g., files under a daas_paid collection on linkeddata.uriburner.com. The 6-step MPP machinery (401 → authenticate → 302 ?k= → 402 challenge → obtain SPT → settle → 200 + receipt) is independent of the authentication protocol used to reach the resource server. WebID-TLS (mTLS) is one protocol option among several — OAuth (Bearer) and Digest are others. Select the protocol by elicitation when it is not clearly discernible from the prompt. In both settlement routes the ACP shop is the merchant of record: it owns the Stripe account and the offer catalog (externalId = offer_iri in the 402 challenge). What differs is the flow: Route A is agent-centric MPP — the agent obtains an SPT from Stripe and presents it to the resource server, which validates the challenge + SPT + ACL and returns the resource with a receipt; Route B is human-centric shop flow — a human user buys via the shop (Stripe subscription), the shop replicates the purchase subset to the resource server, and the user then accesses the resource authenticated.

Reorient after an initial 401

If the first interaction with a protected resource returns 401, immediately send an unauthenticated HTTP OPTIONS request to that same target URL before selecting an authentication protocol:

curl -sS -X OPTIONS -D - "{resource-url}"

Inspect the response for Allow, Link relations, and offer/store discovery metadata. Follow relevant advertised relations to find the associated offer catalog or shop, then continue the appropriate ACP/MPP flow. If OPTIONS also returns 401, use only metadata actually exposed and continue to the auth protocol selection below. This is a discovery probe; it does not authenticate, make a purchase, or authorize a retry.

Auth Protocol Selection (Elicitation)

Pick the authentication protocol before acting. Ask the user if not inferable from the prompt:

Elicitation prompt when ambiguous:

"This paid resource is protected by MPP and supports multiple authentication protocols. Which should I use: (1) WebID-TLS (mTLS), (2) OAuth (Bearer), or (3) Digest?"

If the user specifies a protocol explicitly, honor it.

RULE — WebID-TLS/NetID-TLS port defaults to 5443 automatically, not by discovery. The instant WebID-TLS (or NetID-TLS — same mechanism) is selected, construct or rewrite the target URL onto port 5443 before the first request. Do not probe port 443 first and fall back to 5443 only after a 401. Port 443 on these resource servers never issues a CertificateRequest during the TLS handshake — it falls straight through to a Digest challenge regardless of what certificate is available, which reads exactly like "this resource has no WebID-TLS option" even when it does. Verified live 2026-08-19 against ods-qa.openlinksw.com: :443 → 401 Digest, no CertificateRequest in the handshake at all; :5443 → CertificateRequest issued, cert accepted, 302 to a ?k=... capability URL, which only then returns the real 402. Full detail in Protocol-Specific Notes below and in the sibling x402-buyer skill's references/protocol.md.

Rewrite only when the URL is on port 443 or has no explicit port. A URL already naming some other explicit port (a local/staging server on a custom port) is left untouched — treat that as a deliberate override, not a miss.

WebID-TLS/NetID-TLS Identity Selection (Elicitation)

Selecting WebID-TLS/NetID-TLS as the protocol picks a TLS mechanism, not a certificate. When more than one WebID-TLS identity is available locally — typically a principal identity and one or more agent delegate identities — elicit which one to present before the first request. Do not default to whichever identity was used most recently in the session, and do not default to the principal's identity, without asking:

Elicitation prompt when ambiguous:

"WebID-TLS is selected. Which identity should I present: (1) your principal WebID, or (2) the agent's own delegate WebID?"

If the user specifies an identity explicitly, honor it, and keep presenting that same identity across every hop and every resource for the remainder of the run — do not re-elicit or silently switch identities mid-run.

RULE — verify the selected identity before the first authenticated request. Resolve the credentials root, then run the cert-modulus verification for the selected party only — Steps 1-3 of agent-rdf-memory/howto/verified-identity.ttl for the principal, or Steps 1 and 4-5 for the agent delegate — confirming the local PKCS#12/PEM's public key modulus matches the cert:modulus published in that identity's own profile.ttl before presenting the certificate. A mismatch or a missing local file is not fatal: mark the identity ⚠️ Unverified, tell the user, and proceed only if they confirm. verified-identity.ttl's own full 12-step protocol (including reciprocal delegation corroboration) is scoped to whoami queries and remains optional here — only the per-party modulus check is mandatory before a purchase/access flow. Gap closed 2026-09-08: prior to this rule, neither the auth-protocol table above nor verified-identity.ttl forced an identity check before commerce operations, which is how an earlier QA campaign ran under the wrong WebID-TLS identity for most of a session despite an explicit instruction to use the agent's own identity.

Settlement Route Selection (Elicitation)

Pick the route before acting. Ask the user if not inferable from the request:

Elicitation prompt when ambiguous:

"This paid resource supports two flows: (A) agent-centric MPP — the agent presents an SPT directly to the resource server which validates it; or (B) human-centric shop flow — a user buys via the shop (Stripe subscription), the shop replicates the purchase to the resource server, and the user accesses the resource authenticated. Which flow should I use?"

Route A — Agent-Centric MPP Flow (non-UI agent)

sequenceDiagram
    participant Agent as Software Agent
    participant RS as Resource Server
    participant StripeSPT as Stripe (SPT)

    rect rgb(255,245,230)
    note over Agent,StripeSPT: Agent-centric MPP Flow
    Agent->>RS: Access resource (no prior purchase)
    RS-->>Agent: 402 Payment Required (challenge)
    Agent->>StripeSPT: Request SPT for challenge
    StripeSPT-->>Agent: SPT token
    Agent->>RS: Retry with SPT credential
    RS->>RS: Validate challenge + SPT + ACL
    RS-->>Agent: 200 OK + receipt
    end

Route A notes:

1. The agent has no prior purchase. The first request hits the resource server unauthenticated (or unentitled) and receives the 402 Payment Required challenge: WWW-Authenticate: Payment id, method=stripe, intent=charge, request=base64(amount, currency, externalId=offer_iri, recipient=shop_iri, methodDetails) plus Link: offer_iri; rel=schema.org/offers.
2. The SPT is obtained out of band from Stripe — in test mode via POST https://api.stripe.com/v1/test_helpers/shared_payment/granted_tokens (payment_method pm_card_visa, usage_limits currency/max_amount, expires_at).
3. Present the SPT by echoing the challenge: Authorization: Payment base64({payload:{spt}, challenge}) on the challenged resource URL. The server decodes payload → spt/request/externalId, validates the challenge + SPT + ACL, writes Purchase(PurchasePending) → PurchaseCompleted to the purchase graph, and settles with Stripe.
4. Success is signalled by 200 OK + Payment-Receipt: receipt header, where receipt = base64url({method:stripe, status:success, timestamp, reference:pi_id}). Re-access with the same challenge replays idempotently.
5. No shop/ACP participant is involved — the resource server settles directly. The ACP shop remains the merchant of record (owns the Stripe account and the offer catalog referenced by externalId).

Route B — Human-Centric Shop Flow (interactive / UI user)

sequenceDiagram
    participant User as Human User
    participant Shop as Shop Server
    participant StripeSub as Stripe (Subscriptions)
    participant RS as Resource Server

    rect rgb(230,250,255)
    note over User,StripeSub: Human-centric Shop Flow
    User->>Shop: Login & select offer
    Shop->>StripeSub: Create subscription
    StripeSub-->>Shop: Subscription active
    Shop-->>RS: Replicate purchase subset
    User->>RS: Access resource (authenticated)
    RS->>RS: Check ACL + purchase + subscription
    RS-->>User: 200 OK (resource)
    end

Route B notes:

1. The human user logs in to the shop and selects an offer. The shop is the merchant of record: it owns the Stripe account and the offer catalog (externalId = offer_iri in the 402 challenge).
2. The shop creates a Stripe subscription for the selected offer on the merchant account. The subscription becomes active once its initial invoice is paid — this is the "Subscription active" step, e.g. via the hosted invoice (subscription_payment link) paid through the browser.
3. The shop replicates the purchase subset to the resource server. The shop writes the entitlement (principal → offer) into the resource server's purchases graph, so the resource server can authorize the buyer without re-contacting the shop.
4. The user accesses the resource authenticated. The resource server checks its ACL plus the purchases graph plus the subscription state, and returns 200 OK (resource) when the entitlement holds.

Protocol-Specific Notes

• WebID-TLS (mTLS): default to :5443, not :443, the moment this protocol is selected — see the RULE in Auth Protocol Selection above. Port 443 returns 401 (WebDAV ACL) even with a valid client cert, because the server never requests one on that port; it isn't a fallback path, it's a dead end for this protocol. Request the resource on https://{host}:5443/... (e.g. https://linkeddata.uriburner.com:5443/...) with the WebID-TLS cert to trigger the 302 ?k=... redirect that precedes the 402 challenge. Present the selected identity's client certificate (per WebID-TLS/NetID-TLS Identity Selection above — principal or agent delegate, never assume principal by default) on every hop — the initial request, the ?k=... follow-up, AND the eventual payment-retry request; the authenticated WebID is the service_id.
• OAuth (Bearer): authenticate with Authorization: Bearer {token} (e.g., ACP_AUTH_TOKEN); for delegated resource access use the On-Behalf-Of header with a bare WebID URI — no angle brackets (angle brackets cause delegation resolution failure, 402/401). The {resource-iri} placeholder uses curly braces conventionally — the actual value is a bare IRI.
• Digest: authenticate with HTTP Digest credentials (username/password) against the WebDAV ACL before MPP 401/402 handling applies.

Shared Implementation Notes (both routes)

1. WebID-TLS session reuse trap: disable TLS session reuse (agent: false) for every hop. Node's default https agent resumes the TLS session on the follow-up ?k= request, and the resource server loses the WebID-TLS principal binding — returning 401 Permission denied to <WebID> instead of the expected 302/402. Each request must use a fresh TLS connection. (Symptom: curl succeeds but Node fails.)
2. Use generous timeouts (~90-170 s per hop); the 302/402 hops on the resource server are slow (30+ s each).

Access Verification

After the SPT settles (Route A) or the shop replicates the purchase subset (Route B), re-run the authenticated probe against the resource server (fresh connection each hop) and check for 200 OK:

• Route A: 200 OK + Payment-Receipt: receipt → access granted (idempotent replay of the completed purchase)
• Route B: 200 OK → access granted (resource server checks ACL + purchase + subscription from the replicated purchase subset)
• 402 / 401 Permission denied to <identity> → purchase not recorded or not yet propagated; retry after cache-propagation delay, then escalate the resource-server → purchase-graph → access-ACL binding server-side.

Error Handling

• 401 Unauthorized → Bearer token missing or invalid; direct user to OAuth applications page
• 404 Not Found → Checkout/cart/order ID does not exist
• 409 Conflict → Idempotency key collision; retry with new UUID
• Stripe errors → Report Stripe error message and raw response
• Missing jq → Fall back to bundled awk JSON parsers (_json_str, _json_total, _json_sub_payment_url)

JSON Helper Functions

The skill bundles three portable JSON extraction functions that work with or without jq:

• _json_str FIELD — extract a top-level string field from stdin JSON
• _json_total — extract amount where type=="total" from the totals array
• _json_sub_payment_url — extract subscription_payment href from links[]

See references/acp-api-operations.md for implementation details.

References

• references/acp-api-operations.md — Full curl recipes for every endpoint
• references/oauth-token-setup.md — Step-by-step manual token guide
• references/product-catalog.md — Offer IRI mappings from TTL sources
• ../ucp-client/references/flow-report-template.md — reusable Markdown template (with Mermaid sequence diagrams) for writing up a UCP/ACP/MPP flow test as a standalone report; use it instead of inventing a new report layout

Anti-Drift Protocol

⛔ PRE-BUILD CHECK: Before producing any curl command or output, re-read the relevant operation section in references/acp-api-operations.md. Confirm headers, body shape, and placeholder substitution. Build to pass — do not retro-fit.

Examples

See examples/checkout-flow.sh and examples/cart-flow.sh for complete executable workflows.

Attribution

Derived from acp_curl.sh — reworked into composable curl recipes for agent use.