@powforge/mcp-l402-gate

Identity-scored Lightning paywall for MCP server operators.

L402 alone proves the caller paid 10 sats. It does not prove the caller has a reputation, has been around for more than 10 minutes, or that pricing one tool call shifts their economics at all. A fresh wallet pays the same 10 sats as a real user.

This package adds a Depth-of-Identity check on top of the L402 invoice. Drop it in front of an MCP tool and a caller has to (a) settle a Lightning invoice and (b) carry a DoI score above your threshold before the tool body runs. Cheap sybils still pay the toll, but the toll plus the per-pubkey reputation requirement is harder to grind than either piece on its own.

See it in action

A clone-and-run example server lives at github.com/zekebuilds-lab/mcp-l402-gate-example. It exposes one tool, bitcoin_data, that fetches the BTC/USD price plus mempool fees from mempool.space, gated by L402 + DoI. Clone it, fill in your LNBits creds, npm start, and you have a Lightning-gated MCP server running locally.

The Gap

Sats4AI's own documentation states the limitation plainly:

"autonomous agents cannot build reputation or receive preferential treatment across sessions."

@powforge/mcp-l402-gate closes that gap by composing L402 payment gating with the DoI oracle's composite identity score. A paying caller is also a known caller, with a per-pubkey reputation that survives across sessions and that costs irreversible work to fake.

Why not just L402

L402 is great wire format, weak abuse control. Recent MCP billing tools (sats4ai-mcp, invinoveritas, l402-kit, 402-mcp, coinopai-mcp) all ship the same 402 -> macaroon -> paid -> tool body flow, and an attacker can replay the flow from a fresh node every minute. coinopai-mcp's own author put it: "x402 is payment transport only. It doesn't handle agent identity, rate negotiation, multi-agent splits, or reputation."

PowForge has been shipping the missing piece. The DoI oracle at https://identity.powforge.dev returns a Schnorr-signed score for any Nostr pubkey, computed from observable irreversible work across four dimensions (social, access, vouch, economic). This package wires that score into the L402 path so a paying caller is also a costly-to-fake caller.

Requirements

• Node >= 18
• An LNBits wallet (URL + invoice/read API key) for the Lightning side
• An accessible PowForge oracle URL (default: https://identity.powforge.dev)

5-line integration (Express)

const express = require('express');
const { mcpL402Middleware } = require('@powforge/mcp-l402-gate');

const app = express();
app.use('/tools/expensive', mcpL402Middleware({
  secret: process.env.GATE_HMAC_SECRET,
  lnbitsUrl: process.env.LNBITS_URL,
  lnbitsApiKey: process.env.LNBITS_INVOICE_KEY,
  satsAmount: 10,
  minScore: 10, // composite >= 10 means "emerging" tier on the oracle
}));

app.post('/tools/expensive', (req, res) => {
  // Reached only when L402 paid AND req.doiScore >= 10
  res.json({ ok: true, doiScore: req.doiScore, l402: req.l402Token });
});

The caller passes their pubkey via the X-Caller-Pubkey header or ?pubkey= query string. v0.1.0 treats this as caller-asserted; v0.2.0 will bind it cryptographically via NIP-98.

MCP tool wrapping

const { mcpL402Tool } = require('@powforge/mcp-l402-gate');

const expensiveTool = mcpL402Tool({
  secret: process.env.GATE_HMAC_SECRET,
  lnbitsUrl: process.env.LNBITS_URL,
  lnbitsApiKey: process.env.LNBITS_INVOICE_KEY,
  satsAmount: 10,
  minScore: 10,
}, {
  name: 'image_render',
  description: 'Render an image. 10 sats. Requires DoI score >= 10.',
  inputSchema: {
    type: 'object',
    properties: {
      prompt: { type: 'string' },
      pubkey: { type: 'string' },
      auth: { type: 'object', properties: { macaroon: { type: 'string' }, preimage: { type: 'string' } } },
    },
    required: ['prompt', 'pubkey'],
  },
}, async (args, ctx) => {
  // Runs only when paid AND ctx.doiScore >= 10
  return { image_url: `https://example/r/${args.prompt}`, billed_to: ctx.doiScore };
});

// Register expensiveTool with your MCP server. On first call without args.auth,
// the tool returns { paid: false, challenge: { macaroon, invoice, ... } }.
// The MCP client pays the invoice, then re-calls with args.auth set.

Config reference

| Field | Default | Notes | |-------|---------|-------| | secret | required | HMAC key for macaroon signing. Rotate periodically. | | lnbitsUrl | required | LNBits base URL. | | lnbitsApiKey | required | LNBits invoice/read key. NEVER pass admin key. | | satsAmount | 10 | Invoice amount per call. | | minScore | 10 | Reject paid callers below this composite score. | | failClosed | true | If oracle errors, reject the call. Set false to fall through with req.doiScoreError. | | oracleUrl | https://identity.powforge.dev | Override for self-hosted oracles. | | scope | mcp-l402-gate:call | L402 macaroon scope. | | ttlSeconds | 600 | Macaroon validity. | | scoreField | composite | Which envelope field to compare to minScore. | | callerPubkeyHeader | x-caller-pubkey | HTTP header carrying the caller's asserted pubkey. | | oracleAuth | optional | {macaroon, preimage} if your oracle is itself L402-paywalled. | | createInvoiceFn | optional | Test seam. Async (memo) => {payment_hash, bolt11}. | | checkPaidFn | optional | Test seam. Async (payment_hash) => boolean. | | lookupScoreFn | optional | Test seam. Async (pubkey) => {composite, rank, depth}. |

Score thresholds (composite)

Same buckets the oracle reports as rank:

| Threshold | Rank | Use it when | |-----------|------|-------------| | 0 | unknown | You only want pay-to-call. Skip this package and use L402 directly. | | 10 | emerging | First-call abuse hurts. Default for most public MCP tools. | | 40 | active | The tool burns real GPU or has expensive side effects. | | 100 | established | Compliance-sensitive or single-tenant SaaS-style endpoints. | | 200 | trusted | High-trust admin tooling. |

Failure modes

| Status | Body | Meaning | |--------|------|---------| | 402 | {error: "payment required", macaroon, invoice, payment_hash} | First call. Pay the invoice, retry with Authorization: L402 <macaroon>:<preimage>. | | 401 | {error: "invalid macaroon", reason} | Macaroon malformed, expired, wrong scope, or wrong signature. | | 401 | {error: "preimage does not match payment hash"} | Preimage failed sha256 check against the macaroon's payment hash. | | 409 | {error: "macaroon already redeemed"} | Replay guard fired. Mint a fresh macaroon. | | 400 | {error: "caller_pubkey_required"} | No X-Caller-Pubkey header or ?pubkey= query. | | 403 | {error: "score_too_low", score, min, rank} | Caller paid but DoI score is below threshold. | | 503 | {error: "oracle_unavailable", mode: "fail_closed"} | Oracle error and failClosed is on (the default). | | 502 | {error: "invoice provider unavailable"} | LNBits unreachable on first-call mint. |

Why this is a separate package

The L402 macaroon mint and verify code, the LNBits client, and the oracle client are all already shipping inside other PowForge packages. The point of @powforge/mcp-l402-gate is to make the composition trivial: one factory, one config object, one middleware OR one tool wrapper. Operators do not have to assemble three packages by hand to get a defended endpoint.

Tests

npm test

16 unit tests, no real network. The macaroon HMAC is real; LNBits and oracle are stubbed.

License

MIT.

Links

• PowForge oracle (live): https://identity.powforge.dev
• Identity SDK: @powforge/identity on npm
• MCP identity tools: @powforge/mcp-identity on npm