Templates

A template defines how an approval is rendered on the approver's device. ATAP uses Microsoft Adaptive Cards — an open, platform-agnostic JSON standard for rich UI cards.

Who provides templates

Templates are provided exclusively by the mediating system (via). Each template carries a JWS proof signed by the via entity.

• Three-party approvals: System provides a signed template via template_url.
• Two-party approvals: No template. The client renders subject.label as title and subject.payload as formatted JSON.

If a template is unavailable or verification fails, the client falls back to the default rendering.

Template format

{
  "atap_template": "1",
  "card": {
    "type": "AdaptiveCard",
    "version": "1.5",
    "body": [
      {
        "type": "TextBlock",
        "text": "${subject.label}",
        "size": "Large",
        "weight": "Bolder"
      },
      {
        "type": "FactSet",
        "facts": [
          { "title": "Product", "value": "${payload.product}" },
          { "title": "Price", "value": "${payload.price.amount} ${payload.price.currency}" }
        ]
      }
    ]
  },
  "proof": {
    "kid": "did:web:merchant.com:machine:checkout#key-1",
    "alg": "EdDSA",
    "sig": "<JWS>"
  }
}

Data binding

Templates use Adaptive Card Templating syntax (${expression}) bound to this context:

{
  "subject": { ... },
  "payload": { ... },
  "brand": { ... },
  "from": "<requester-DID>",
  "to": "<approver-DID>",
  "via": "<system-DID>"
}

Template verification

1. Fetch template from template_url.
2. Extract proof.kid. The DID must match the via entity's DID.
3. Resolve the DID Document, extract the public key.
4. Verify JWS over the template (excluding proof).
5. On success: bind data and render. On failure: fallback.

Verified templates may be cached indefinitely — the signature guarantees integrity.

Security

• HTTPS only. No redirects.
• Maximum response size: 64 KB. Fetch timeout: 5 seconds.
• Action.Submit and Action.OpenUrl must be disabled. Only the native Approve/Decline buttons are allowed.
• Block private IPs (RFC 1918, loopback, link-local, cloud metadata).