extensions object.
Use extensions when a server requires additional fields beyond core payment data, such as authentication, idempotency, or discovery metadata.
Built-in Extensions
- Sign-In-With-X (
siwx) for wallet-authenticated access - Payment Identifier (
paymentIdentifier) for idempotency - Bazaar (
bazaar) for discovery metadata
Extension Flow
- Server declares required extensions in
PAYMENT-REQUIRED - Client hooks inspect required extension metadata
- Client adds extension payload fields before signing
- Server verifies and processes extension data