@nikhilraikwar/mcpay

Implements RFC 7231 HTTP 402 Payment Required status code enforcement as Express middleware, intercepting requests to MCP tool servers and validating payment credentials before allowing tool execution. Uses OWS CLI integration to verify payment state and enforce monetization policies at the HTTP layer, blocking unpaid requests with 402 responses and payment metadata.

Integrates USDC stablecoin payments on the Base blockchain through OWS CLI, enabling tool servers to accept and validate on-chain payments without directly managing wallet keys or smart contracts. Abstracts blockchain interaction complexity by delegating to OWS CLI's payment verification and settlement logic.

Provides a Node.js wrapper around OWS CLI commands for payment validation, executing CLI subcommands to check payment status, retrieve payment metadata, and enforce monetization policies. Uses child_process spawning to invoke OWS CLI with structured arguments and parses JSON responses for payment state verification.

Exports a middleware factory function that creates Express middleware instances configured with specific payment requirements (amount, currency, recipient). Middleware intercepts requests, validates payment state via OWS CLI, and either forwards requests to downstream tools or returns 402 responses with payment instructions.

Parses OWS CLI responses and formats payment metadata (transaction hash, amount, timestamp, payer address) into HTTP response headers and JSON bodies for 402 Payment Required responses. Structures payment instructions in a standardized format that clients can use to complete payment and retry requests.

Enforces configurable monetization policies at the MCP server level, including minimum payment amounts, payment recipient addresses, and currency requirements. Policies are applied per-middleware instance and validated against incoming requests before tool execution is allowed.