X402 example

[1evi7eo]

Description

Adds an x402 payment protocol implementation on BNB Chain, demonstrating HTTP 402 "Payment Required" for internet-native payments with sign-to-pay.

This example:

• Implements the x402 standard using HTTP 402 status codes
• Demonstrates EIP-712 signature-based payment authorization
• Shows sign-to-pay without API keys, registrations, or KYC
• Includes payment request creation, signature verification, and on-chain execution
• Provides an interactive web frontend for testing x402 payments
• Integrates with MCP for AI agent interactions

Motivation: x402 enables autonomous payments between AI agents, APIs, and services. This implementation shows how to use HTTP 402, EIP-712 signatures, and blockchain payments to create a payment flow without traditional authentication.

Type of change

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Unit tests: pytest test_x402_payment.py -v — all 10 tests pass
• Manual testing:
  • Started server with ./run.sh
  • Verified frontend loads at http://localhost:5001
  • Created payment requests and verified EIP-712 signature generation
  • Tested signature verification with valid and invalid signatures
  • Executed payments and verified on-chain transaction completion
  • Tested payment status tracking and history
• Integration testing:
  • Tested MCP tool integration (create_payment_request, verify_payment_signature, execute_payment, get_payment_status, list_payment_requests)
  • Verified virtual environment setup and dependency installation
  • Confirmed EIP-712 typed data signing works correctly
  • Tested payment request uniqueness with counter-based ID generation
  • Verified error handling for invalid addresses, signatures, and payment states

Test coverage includes:

• Payment request creation with EIP-712 signatures
• Signature verification and validation
• Payment execution on-chain
• Payment status tracking
• Payment history and filtering
• Error handling for edge cases

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Additional Notes

• Implements EIP-712 typed data signing for cryptographic payment authorization
• Demonstrates HTTP 402 "Payment Required" status code usage
• Includes interactive frontend for testing the complete payment flow
• Full MCP protocol support for AI agent integration
• Comprehensive README with demo examples and usage instructions
• Virtual environment setup script for easy deployment
• All dependencies documented in requirements.txt
• Fixed payment ID uniqueness issue using counter-based generation to prevent collisions

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