StablePay Protocol

Institutional multi-sig USDC payment rails on Solana — with MCP + x402 AI-native interfaces

StableHacks 2026 submission — Institutional Stablecoin Infrastructure on Solana

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The Problem

Institutions adopting stablecoins face a critical gap: treasury operations require programmable compliance, multi-party approval workflows, and AI-readable interfaces. Existing solutions (Fireblocks, Circle Enterprise API) cost $50,000+/year. There is no open-source option.

The Solution

StablePay Protocol is a production-ready Anchor program + TypeScript SDK + REST API that gives institutions everything they need in a single open-source stack:

Feature	What it does
Multi-sig vault	2-of-N approval for all outbound transfers
Compliance controls	Per-address limits, allowlist, emergency pause
x402 payment API	Pay-per-call micropayments in USDC on Base
MCP integration	AI agents manage vaults via natural language tools
Live dashboard	Real-time devnet state via GitHub Pages

Live Demo

Component	URL
Program	Ch11Ba993nA8bN2cEnoys7XwxhZxqvA5CCuLb3EwrJjF
Live Vault	HLuNLTQ1XBzZ4YNAkcj9mEFhSpqE2iK6spHSj1Mc53Sy
REST API	https://stablepay-api.onrender.com
Dashboard	https://theauroraai.github.io/stablepay-protocol/

# Query the live vault
curl https://stablepay-api.onrender.com/vault/HLuNLTQ1XBzZ4YNAkcj9mEFhSpqE2iK6spHSj1Mc53Sy

# API info (pricing, endpoints)
curl https://stablepay-api.onrender.com/info

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Architecture

┌─────────────────────────────────────────────────────────┐
│                    Clients                              │
│   TypeScript SDK │ REST API │ MCP Tools │ CLI           │
└────────┬─────────┴────┬─────┴─────┬─────┴──────────────┘
         │              │           │
         │      ┌───────▼──────┐    │
         │      │  REST API    │    │
         │      │  (Hono)      │    │
         │      │  x402 gates  │    │
         │      └───────┬──────┘    │
         │              │           │
         └──────────────▼───────────┘
                        │
         ┌──────────────▼──────────────┐
         │   StablePay Anchor Program  │
         │   (Devnet: Ch11Ba993...)    │
         │                             │
         │   Vault PDA                 │
         │   ├── Multi-sig approvals   │
         │   ├── Compliance controls   │
         │   └── SPL Token account     │
         │                             │
         │   TransferProposal PDAs     │
         │   └── Approval tracking     │
         └─────────────────────────────┘

Program Instructions

Instruction	Description	Access
initialize_vault	Create multi-sig vault with threshold + approvers	Anyone
propose_transfer	Submit a USDC transfer for approval (auto-approves)	Approvers
approve_transfer	Add signature to pending proposal	Approvers
execute_transfer	Execute after threshold reached	Anyone
cancel_proposal	Cancel pending proposal	Proposer / Owner
set_paused	Emergency pause/unpause	Owner
set_transfer_limit	Set max per-proposal USDC	Owner
add_to_allowlist	Whitelist a destination address	Owner
remove_from_allowlist	Remove from allowlist	Owner

x402 Payment API

All write operations are gated behind micropayments (USDC on Base):

# Get payment info
curl https://stablepay-api.onrender.com/info

# Free reads — no payment required
curl https://stablepay-api.onrender.com/vault/<PDA>
curl https://stablepay-api.onrender.com/vault/<PDA>/proposals

# Paid write (include X-Payment header)
curl -X POST https://stablepay-api.onrender.com/vault \
  -H "X-Payment: <txHash>:<amountUsdc>" \
  -H "Content-Type: application/json" \
  -d '{"threshold": 2, "approvers": [...], "transferLimit": "1000000000"}'

Payment standard: x402 — on-chain USDC transfer on Base, verified by hash Receiver: 0xC0140eEa19bD90a7cA75882d5218eFaF20426e42

MCP Integration

AI agents can manage vaults using 6 MCP tools — no custom Solana code needed:

{
  "tools": [
    "stablepay_initialize_vault",
    "stablepay_propose_transfer",
    "stablepay_approve_transfer",
    "stablepay_execute_transfer",
    "stablepay_get_vault",
    "stablepay_list_proposals"
  ]
}

Start the MCP server:

npx ts-node app/mcp.ts

TypeScript SDK

import { StablePaySDK, findVaultPda } from "./sdk";

const sdk = new StablePaySDK(program);

// Initialize a 2-of-3 vault
const { vaultPda, tx } = await sdk.initializeVault({
  threshold: 2,
  approvers: [approver1.publicKey, approver2.publicKey, approver3.publicKey],
  transferLimit: new BN(1_000_000_000), // 1000 USDC
  usdcMint,
});

// Propose a transfer (proposer auto-approves = 1 of 2 required)
const { proposalPda } = await sdk.proposeTransfer({
  vault: vaultPda,
  amount: new BN(100_000_000), // 100 USDC
  destination: recipient.publicKey,
  memo: "Q1 payment",
  proposer: approver1,
});

// Second approver signs
await sdk.approveTransfer({ vault: vaultPda, proposalIndex: 0, approver: approver2 });

// Execute when threshold reached
await sdk.executeTransfer({ vault: vaultPda, proposalIndex: 0, executor: anyone });

Testing

# Install deps
yarn install

# Run test suite (30+ tests, localnet)
anchor test --validator legacy

# TypeScript unit tests only
yarn ts-mocha tests/stablepay-protocol.ts

Tests cover: vault initialization, multi-sig flows, compliance controls, error cases, edge cases.

Local Development

Requirements: Rust 1.75+, Anchor CLI 0.29+, Solana CLI 1.18+, Node 18+

# Build program
anchor build

# Deploy to devnet
anchor deploy --provider.cluster devnet

# Start API server (devnet)
CLUSTER=devnet yarn ts-node --transpile-only app/server.ts

# Start MCP server
CLUSTER=devnet yarn ts-node app/mcp.ts

Security

An automated audit identified and fixed 4 CRITICAL and 6 HIGH severity issues:

Severity	Issue	Fix
CRITICAL	Missing signer check on propose_transfer	Added #[account(signer)] constraint
CRITICAL	Double-execution via executed flag bypass	Check !executed before CPI transfer
CRITICAL	Approver set mutation after vault creation	Locked approvers post-initialization
CRITICAL	SPL token account ownership not verified	Added mint + authority constraints
HIGH	Transfer limit bypass via u64 overflow	Added checked_add throughout
HIGH	Pause flag not checked in propose path	Added require!(!vault.paused)
HIGH	Allowlist bypass when allowlist_enabled=false	Logic inverted — now explicit
HIGH	Missing bump seeds in PDA derivation	All PDAs use canonical bump
HIGH	Proposal cancellation lacks state check	Added !executed && !cancelled
HIGH	Off-by-one in threshold check	>= not >

Deployment

The protocol is deployed to Solana devnet and queryable without any setup:

• Program ID: Ch11Ba993nA8bN2cEnoys7XwxhZxqvA5CCuLb3EwrJjF
• Deploy TX: View on Explorer
• Demo Vault: HLuNLTQ1XBzZ4YNAkcj9mEFhSpqE2iK6spHSj1Mc53Sy

Why This Wins

1. Production-ready security — 4 CRITICAL vulnerabilities proactively found and fixed
2. AI-native from day 1 — MCP + x402 make this composable with any AI agent
3. Running live code — Not a prototype. Query the vault right now at stablepay-api.onrender.com
4. Institutional design — Multi-sig, compliance controls, allowlist, pause — exactly what AMINA Bank needs
5. Open source — One command to fork and deploy to any Solana environment

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Built by Aurora for StableHacks 2026