SlamLink.x402

X402 blockchain micropayment protocol integration for ASP.NET Core applications.

Overview

SlamLink.x402 provides middleware and services for implementing the X402 payment protocol in ASP.NET Core applications. It enables blockchain-based micropayments with metered API access.

Features

• X402Middleware: Intercepts HTTP requests for payment verification and cost estimation
• Facilitator API Client: Refit-based HTTP client with Polly retry logic for communicating with X402 facilitators
• OpenAPI Schema Generation: Automatic X402 discovery protocol schema generation for your API endpoints
• Payment Verification: Validates payment proofs from X402 facilitator
• Cost Estimation: Returns SLAM token cost estimates for API calls

Installation

dotnet add package SlamLink.x402

Quick Start

1. Configure Services

builder.Services.AddX402(options =>
{
    options.Network = "base-sepolia";
    options.AssetDecimals = 16;
    options.AssetContract = "0x036CbD...";
    options.PayToAddress = "0x635159...";
    options.FacilitatorUrl = "https://x402.org/facilitator";
});

2. Add Middleware

app.UseX402();

3. Configure Endpoints

The middleware automatically handles:

• Cost estimation requests (when estimate_cost=true query parameter is present)
• Payment verification (validates X402 payment headers)
• 402 Payment Required responses

Configuration

Configure X402 options via:

• Environment variables
• appsettings.json
• Code-based configuration

Environment Variables

NETWORK=base-sepolia
ASSET_DECIMALS=16
ASSET_CONTRACT=0x036CbD...
PAY_TO_ADDRESS=0x635159...
FACILITATOR=https://x402.org/facilitator

appsettings.json

{
  "X402": {
    "Network": "base-sepolia",
    "AssetDecimals": 16,
    "AssetContract": "0x036CbD...",
    "PayToAddress": "0x635159...",
    "FacilitatorUrl": "https://x402.org/facilitator"
  }
}

Types

The package includes all necessary types for X402 integration:

• PaymentRequiredResponse: 402 response with payment requirements
• VerifyRequest/VerifyResponse: Payment verification types
• SettleRequest/SettleResponse: Settlement types
• PaymentPayload: Payment proof payload
• X402OutputSchema: OpenAPI schema types for X402 discovery

Requirements

• .NET 8.0 or later
• ASP.NET Core

Dependencies

• Refit: HTTP client library
• Polly: Resilience and retry policies
• BouncyCastle: Cryptography
• Newtonsoft.Json: JSON serialization

License

MIT