TAP-MCP Bridge

Rust library and MCP server for Visa's Trusted Agent Protocol (TAP), enabling AI agents to securely authenticate with merchants and execute payment transactions.

Workspace Structure

Installation

As a Library

[dependencies]
tap-mcp-bridge = "0.1"

As MCP Server

cargo install --path tap-mcp-server

Configure your MCP client (Claude Desktop, etc.):

{
  "mcpServers": {
    "tap": {
      "command": "tap-mcp-server",
      "env": {
        "TAP_AGENT_ID": "your-agent-id",
        "TAP_AGENT_DIRECTORY": "https://your-agent-directory.com",
        "TAP_SIGNING_KEY": "64-hex-characters-ed25519-key"
      }
    }
  }
}

[!IMPORTANT] Requires Rust 1.85+ (Edition 2024).

Quick Example

use ed25519_dalek::SigningKey;
use tap_mcp_bridge::tap::{InteractionType, TapSigner};

let signing_key = SigningKey::from_bytes(&[0u8; 32]);
let signer = TapSigner::new(signing_key, "agent-123", "https://agent.example.com");

let signature = signer.sign_request(
    "POST",
    "merchant.example.com",
    "/checkout",
    b"request body",
    InteractionType::Checkout,
)?;

println!("Signature: {}", signature.signature);
println!("Signature-Input: {}", signature.signature_input);

MCP Tools

The server exposes three tools for AI agents:

Features

TAP Protocol

• RFC 9421 HTTP Message Signatures with Ed25519
• RFC 7516 JWE encryption for payment data (A256GCM + RSA-OAEP-256)
• RFC 7638 JWK Thumbprints for key identification
• ID Tokens (JWT) for consumer authentication
• ACRO — Agentic Consumer Recognition Object
• APC — Agentic Payment Container with JWE encryption

Production Features

• Retry with backoff — Exponential backoff with jitter for transient failures
• Circuit breaker — Protection against cascading failures
• Rate limiting — Token bucket algorithm for request throttling
• Audit logging — Structured security events with sensitive data redaction
• Prometheus metrics — Request counters, error rates, latency tracking
• Replay protection — UUID v4 nonce with LRU cache validation

Examples

# Basic checkout flow
cargo run --example basic_checkout

# Browse merchant catalog
cargo run --example browse_catalog

# Error handling patterns
cargo run --example error_handling

# TAP signature generation
cargo run --example signature_generation

# JWKS for agent directory
cargo run --example jwks_generation

# ID Token (JWT) generation
cargo run --example id_token_generation

# ACRO generation
cargo run --example acro_generation

# APC encryption/decryption
cargo run --example apc_generation

[!TIP] Set AGENT_SIGNING_KEY environment variable before running examples:

export AGENT_SIGNING_KEY=$(openssl rand -hex 32)

Documentation

Development

# Install tools
cargo install cargo-nextest cargo-make cargo-deny

# Quick verification
cargo make pre-commit

# Full test suite (200+ tests)
cargo nextest run --all-features

# Security audit
cargo deny check

# Documentation
cargo doc --no-deps --open

License

Licensed under MIT OR Apache-2.0 at your option.

Resources

• TAP Protocol — Official Visa documentation
• MCP Protocol — Anthropic's Model Context Protocol
• RFC 9421 — HTTP Message Signatures
• RFC 7516 — JSON Web Encryption (JWE)