Transports
HTTP, MCP, and WebSocket bindings for payment flows
MPP defines how the Payment authentication scheme operates over different transport protocols. The core protocol targets HTTP, with extensions for other transports like MCP and JSON-RPC.
Available transports
| Transport | Use Case | Spec |
|---|---|---|
| HTTP | REST APIs, web resources | RFC 9110 |
| MCP | AI tool calls using Model Context Protocol | MCP Transport Spec |
| WebSocket | Bidirectional payment streams | RFC 6455 |
| JSON-RPC | Non-MCP JSON-RPC services | JSON-RPC 2.0 |
Transport-agnostic design
MPP's core concepts—Challenges, Credentials, and Receipts—remain the same across transports. The encoding and delivery mechanism changes:
- HTTP uses standard headers (
WWW-Authenticate,Authorization,Payment-Receipt) - MCP uses JSON-RPC error codes and
_metafields - WebSocket uses JSON message framing with an
mppdiscriminator
Choose the transport that matches your protocol. HTTP for REST APIs, MCP for AI agent tool calls, WebSocket for bidirectional payment streams, or JSON-RPC for non-MCP JSON-RPC services.