Tollgate

Pay-per-use WireGuard VPN gateway for autonomous agents. No subscriptions, no pre-auth — each access is gated by a USDC micropayment verified on Base.

Flow: agent hits /vpn → gets 402 → pays 0.01 USDC on Base Sepolia via Openfort → retries with tx hash → receives WireGuard peer config valid for 1 hour.

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Use cases

Tollgate is built for programmatic, pay-per-use VPN access — no accounts, no subscriptions, no human in the loop. The x402 protocol makes it native to any agent or automated system that can send a USDC transaction.

Use case	Why x402 fits
Autonomous AI agents	An agent hits a geo-restricted API, receives a 402, pays, and retries — entirely without human intervention
CI/CD pipelines	Build jobs pay only for the minutes they need VPN access; no standing subscription tied to infrastructure
Web scraping / data collection	Each agent session gets a fresh peer IP; pay per crawl run rather than managing a pool of proxies
Multi-agent systems	Many agents coordinate independently — each pays for its own session with no shared credentials or API keys to rotate
Privacy-sensitive upstream calls	Agents mask the operator's origin IP when calling third-party APIs, without exposing a persistent VPN identity
IoT / embedded devices	Low-cost devices that need occasional secure tunneling; per-use micropayments are more economical than monthly plans
Temporary developer access	A dev needs VPN access for one hour during an incident — pays $0.01 instead of provisioning a full subscription

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How it works

Payment protocol (x402)

Tollgate implements the x402 payment protocol. When an agent hits GET /vpn without a payment header, the server returns a 402 Payment Required with a JSON body describing exactly what to pay, to whom, and on which network. The agent pays, then retries with X-Payment: <txHash>. The server verifies on-chain before provisioning access.

Agent wallet (Openfort)

The agent script uses Openfort backend wallets to send USDC programmatically — no private keys in env vars, no manual signing. Openfort handles key custody, gas sponsorship, and ERC-4337 account abstraction under the hood.

On-chain verification

The server uses Alchemy to fetch the transaction receipt from Base Sepolia and parses the ERC-20 Transfer event logs to verify:

• Transfer was sent to PAYMENT_RECIPIENT_ADDRESS
• Amount ≥ PAYMENT_AMOUNT_USDC
• USDC contract matches USDC_CONTRACT_ADDRESS

Because Openfort uses a bundler/paymaster, there can be a few seconds of indexing lag between when the UserOperation is confirmed and when Alchemy's RPC node returns the receipt. The server retries up to 4 times with 5s intervals before rejecting.

Replay protection

Each tx hash is stored in Redis with a 7-day TTL. Submitting the same hash twice returns a 402.

WireGuard provisioning

On successful payment, the server generates a unique keypair via the wg CLI, allocates an IP from 10.0.0.10–10.0.0.209, adds the peer to the wg0 interface, stores the session in Redis, and returns the client config string.

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Network

Currently running on Base Sepolia (testnet) — chainId 84532, USDC 0x036CbD53842c5426634e7929541eC2318f3dCF7e.

Mainnet constants are commented in scripts/agent-sim.ts and src/services/payment.ts — swap them in when a live Openfort key is available.

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Stack

• Node.js (ESM, LTS) · Express · TypeScript · tsx
• ethers.js v6 · ioredis · pino · express-rate-limit
• WireGuard (managed via wg CLI, no shell — execFileSync)
• Openfort (@openfort/openfort-node) — backend wallet for agent payments
• Base Sepolia (testnet) · USDC 0x036CbD53842c5426634e7929541eC2318f3dCF7e

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Quick start (local dev)

Prerequisites

• Node.js 20+
• Redis running locally (brew services start redis on macOS)
• An Alchemy API key (Base Sepolia)
• A Base wallet address to receive payments
• An Openfort account with a backend wallet configured

Install

npm install

Configure

cp .env.example .env

Fill in .env. Minimum required to start:

PORT=3002
REDIS_URL=redis://127.0.0.1:6379
ALCHEMY_API_KEY=your_key_here
PAYMENT_RECIPIENT_ADDRESS=0xYourWalletAddress
BASE_CHAIN_ID=84532
USDC_CONTRACT_ADDRESS=0x036CbD53842c5426634e7929541eC2318f3dCF7e

Run

npm start          # production entry point (src/main.ts)
npm run dev        # auto-restarts on file changes
npm run typecheck  # type check without running

Test

npm test           # runs all tests (uses PAYMENT_STUB and WG_STUB — no Alchemy or wg needed)

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Agent simulation (end-to-end test)

Simulates an autonomous agent paying USDC via Openfort and receiving a WireGuard config.

Prerequisites

• Tollgate server running (npm start)
• An Openfort backend wallet account funded with:
  • Test ETH on Base Sepolia (gas) — Alchemy faucet
  • Test USDC on Base Sepolia — Circle faucet

Set up Openfort backend wallet

Create a backend wallet account (one-time setup):

node --input-type=module << 'EOF'
import 'dotenv/config';
import Openfort from '@openfort/openfort-node';
const of = new Openfort(process.env.OPENFORT_SECRET_KEY, { walletSecret: process.env.OPENFORT_WALLET_SECRET });
const account = await of.accounts.evm.backend.create({ chainId: 84532 });
console.log('OPENFORT_ACCOUNT_ID=' + account.id);
console.log('Wallet address:      ' + account.address);
EOF

Fund the printed wallet address via the faucets above, then add the account ID to .env.

Configure

Add to .env:

OPENFORT_SECRET_KEY=sk_...
OPENFORT_WALLET_SECRET=...
OPENFORT_ACCOUNT_ID=acc_...
TOLLGATE_URL=http://your-server:3002

Run

node --import tsx/esm scripts/agent-sim.ts

Expected output:

[1] GET http://your-server:3002/vpn
[1] 402 received — payment required: 0.01 USDC to 0x...

[2] Checking USDC contract registration in Openfort...
[2] USDC already registered: con_...

[3] Sending 0.01 USDC → 0x... via Openfort...
[3] Confirmed — tx: 0x...

[4] GET http://your-server:3002/vpn with X-Payment: 0x...
[4] 200 received — WireGuard config provisioned
    Session ID : <uuid>
    Allowed IP : 10.0.0.x
    Expires in : 3600s

[5] Tollgate access provisioned.
    WireGuard config : /tmp/tollgate-client.conf
    Receipt          : /tmp/tollgate-receipt.json

    Connect with: sudo wg-quick up /tmp/tollgate-client.conf

── Openfort ────────────────────────────────────────────────────────────
    Intent ID      : tin_...
    Account        : acc_...

Connect the tunnel

sudo wg-quick up /tmp/tollgate-client.conf

# Disconnect
sudo wg-quick down /tmp/tollgate-client.conf

Expire a session manually

node --import tsx/esm scripts/expire-test.ts <sessionId>

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Production deployment (Ubuntu VPS)

Install dependencies

sudo apt update && sudo apt install wireguard redis-server -y
curl -fsSL https://deb.nodesource.com/setup_20.x | sudo -E bash -
sudo apt install -y nodejs
npm install -g pm2

WireGuard server setup

# Generate server keypair
wg genkey | tee /etc/wireguard/server_private.key | wg pubkey > /etc/wireguard/server_public.key

# Create interface config (replace YOUR_PRIVATE_KEY and eth0 if needed)
cat > /etc/wireguard/wg0.conf << EOF
[Interface]
Address = 10.0.0.1/24
ListenPort = 51820
PrivateKey = YOUR_PRIVATE_KEY

PostUp   = iptables -A FORWARD -i wg0 -j ACCEPT; iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
PostDown = iptables -D FORWARD -i wg0 -j ACCEPT; iptables -t nat -D POSTROUTING -o eth0 -j MASQUERADE
EOF

# Enable IP forwarding
echo "net.ipv4.ip_forward=1" | tee -a /etc/sysctl.conf && sysctl -p

# Start WireGuard
systemctl enable wg-quick@wg0 && systemctl start wg-quick@wg0

Deploy and run

# Copy project to server
scp -r /path/to/tollgate user@your-server:~/tollgate

# On the server
cd ~/tollgate
cp .env.example .env && nano .env   # fill in all values
npm install

pm2 start src/main.ts --name tollgate --cwd ~/tollgate --interpreter tsx
pm2 save
pm2 startup

Firewall

ufw allow 22/tcp
ufw allow 3002/tcp
ufw allow 51820/udp
ufw enable

Production security checklist

Before going live, make sure these are set in your production .env:

Setting	Production value	Why
STRICT_REPLAY_CHECK	true	Prevents replay attacks if Redis restarts — fails closed (503) instead of open
PUBLIC_HOST	https://your-domain.com	Ensures the 402 resource URL is correct behind a reverse proxy
PAYMENT_AMOUNT_USDC	your chosen price	Default 0.01 — adjust for mainnet economics

Additional hardening in place out of the box:

• Rate limiting — /vpn is limited to 20 requests per IP per minute via express-rate-limit. Tune max in src/server.ts for your expected traffic.
• No shell execution — all wg CLI calls use execFileSync with explicit argument arrays, eliminating shell injection surface.
• API key redaction — Alchemy RPC errors are sanitised before being returned to clients; the API key is never exposed in 402 responses.
• Peer lifecycle safety — if Redis is unavailable when storing a new session, the WireGuard peer is rolled back (wg set … remove) before the 500 is returned, preventing zombie peers.

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Architecture

Request flow

flowchart TD
    A([Agent]) --> B[GET /vpn]
    B --> C{Rate limit\nexceeded?}
    C -->|Yes| D[429 Too Many Requests]
    C -->|No| E{X-Payment\nheader?}
    E -->|Missing| F[402 + payment JSON\nx402 middleware]
    E -->|Present txHash| G[payment.ts\nAlchemy → Base Sepolia\nretry up to 4×5s]
    G -->|Invalid| H[402 + reason]
    G -->|Valid| I[replay.ts → Redis\nreplay check + mark used]
    I -->|Duplicate TX| J[402 Already used]
    I -->|Fresh TX| K[wireguard.ts\ngenkey · allocateIP · addPeer]
    K --> L[session.ts → Redis\nTTL = SESSION_TTL_SECONDS]
    L --> M[200 + WireGuard config]

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Security layers

flowchart LR
    subgraph L1[Layer 1 — Network]
        A[UFW Firewall\nports 22 · 3002 · 51820]
    end
    subgraph L2[Layer 2 — Rate Limiting]
        B[express-rate-limit\n20 req / IP / min]
    end
    subgraph L3[Layer 3 — Payment Gate]
        C[x402 middleware\n402 challenge]
    end
    subgraph L4[Layer 4 — On-chain Verification]
        D[Alchemy RPC\nTransfer event · amount · recipient]
    end
    subgraph L5[Layer 5 — Replay Protection]
        E[Redis\nTX hash · 7-day TTL]
    end
    subgraph L6[Layer 6 — Peer Safety]
        F[Rollback on Redis failure\nno zombie peers]
    end
    A --> B --> C --> D --> E --> F

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Environment variables

Variable	Description
BASE_CHAIN_ID	Chain ID for payment verification. Default 84532 (Base Sepolia). Set to 8453 for mainnet.
USDC_CONTRACT_ADDRESS	USDC contract address for the configured chain. Default 0x036CbD... (Base Sepolia).
PAYMENT_RECIPIENT_ADDRESS	Wallet address that receives USDC payments.
PAYMENT_AMOUNT_USDC	Price per access in USDC. Default 0.01.
SESSION_TTL_SECONDS	How long a provisioned WireGuard peer stays active. Default 3600 (1 hour).
STRICT_REPLAY_CHECK	true = fail closed if Redis is down (prevents replay attacks). Default false. Set to true in production.
PUBLIC_HOST	Set to your public URL when behind a reverse proxy — used in the 402 resource field.

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Next steps

flowchart LR
    D1([Day 1 ✓\nCore Gateway]) --> D2[Day 2\nSession Lifecycle]
    D2 --> a[Session expiry daemon]
    D2 --> b[WireGuard peer cleanup]
    D2 --> c[Rate limiting per wallet]
    D2 --> d[IP pool hardening]
    D2 --> e[Status dashboard]
    D2 --> D3[Day 3\nMainnet & Scale]
    D3 --> f[Swap to Base mainnet]
    D3 --> g[Live Openfort key]
    D3 --> h[WireGuard concurrency queue]
    D3 --> i[Reverse proxy + TLS]

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