Skip to main contentx402 extensions are protocol-level metadata attached to challenges and payment payloads via the 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
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