SIWA Bankr Signer

Sign SIWA messages using Bankr's Agent API wallets.

Install

npm install @buildersgarden/siwa

No additional SDK is required — the Bankr signer communicates directly with the Bankr Agent API over HTTP.

Create Signer

import { createBankrSiwaSigner } from "@buildersgarden/siwa/signer";

const signer = await createBankrSiwaSigner({
  apiKey: process.env.BANKR_API_KEY!,
});

The wallet address is fetched automatically from Bankr's /agent/me endpoint.

Register as ERC-8004 Agent

Bankr wallets are smart contract accounts (ERC-4337). To register on the ERC-8004 Identity Registry, submit the registration as an arbitrary transaction via Bankr's /agent/submit endpoint.

Supported Networks

The Bankr /agent/submit endpoint supports these chains:

| Network | Chain ID | |------------|----------| | Ethereum | 1 | | Polygon | 137 | | Base | 8453 | | Unichain | 130 |

Transaction Format

The /agent/submit endpoint requires a transaction object with these fields:

| Field | Type | Description | |-----------|--------|---------------------------------------------------------| | to | string | Contract address (0x + 40 hex characters) | | data | string | ABI-encoded calldata (0x-prefixed, or "0x" if empty)| | value | string | Transaction value in wei (use "0" for registration) | | chainId | number | Target network ID (must be a supported network above) |

Example

import { encodeRegisterAgent } from "@buildersgarden/siwa/registry";

// Prepare agent metadata
const metadata = {
  name: "My Agent",
  description: "A helpful AI assistant",
  capabilities: ["chat", "analysis"],
};
const agentURI = `data:application/json;base64,${Buffer.from(JSON.stringify(metadata)).toString("base64")}`;

// Encode the registration calldata (resolves the registry address automatically)
const { to, data } = encodeRegisterAgent({ agentURI, chainId: 8453 });

// Submit as arbitrary transaction via Bankr API
const submitRes = await fetch("https://api.bankr.bot/agent/submit", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    "X-API-Key": process.env.BANKR_API_KEY!,
  },
  body: JSON.stringify({
    transaction: { to, data, value: "0", chainId: 8453 },
    waitForConfirmation: true,
  }),
});

const result = await submitRes.json();
console.log("Transaction hash:", result.txHash);

Important: Transactions submitted via /agent/submit are irreversible. Always verify calldata encoding and confirm the target contract address before submitting. Ensure the wallet has sufficient ETH/MATIC for gas. The endpoint handles UserOperation bundling internally for ERC-4337 smart accounts, and SIWA verification uses ERC-1271 automatically.

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SIWA Authentication Flow

The authentication flow consists of two steps:

Note: The URLs below (api.example.com) are placeholders. Replace them with your own server that implements the SIWA verification endpoints. See the Server-Side Verification skill for implementation details.

1. Get a nonce from the server's /siwa/mainnet/nonce endpoint
2. Sign and verify by sending the signature to /siwa/mainnet/verify

Step 1: Request Nonce

const nonceRes = await fetch("https://api.example.com/siwa/mainnet/nonce", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    address: await signer.getAddress(),
    agentId: 42,
    agentRegistry: "eip155:8453:0x8004A169FB4a3325136EB29fA0ceB6D2e539a432",
  }),
});
const { nonce, nonceToken, issuedAt, expirationTime } = await nonceRes.json();

Step 2: Sign and Verify

import { signSIWAMessage } from "@buildersgarden/siwa";

const { message, signature, address } = await signSIWAMessage({
  domain: "api.example.com",
  uri: "https://api.example.com/siwa",
  agentId: 42,
  agentRegistry: "eip155:8453:0x8004A169FB4a3325136EB29fA0ceB6D2e539a432", //According to the chain
  chainId: 8453,
  nonce,
  issuedAt,
  expirationTime,
}, signer);

// Send to server for verification
const verifyRes = await fetch("https://api.example.com/siwa/mainnet/verify", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ message, signature, nonceToken }),
});

const { receipt, agentId } = await verifyRes.json();
// Store the receipt for authenticated API calls

Sign Authenticated Request (ERC-8128)

import { signAuthenticatedRequest } from "@buildersgarden/siwa/erc8128";

const request = new Request("https://api.example.com/action", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ action: "execute" }),
});

const signedRequest = await signAuthenticatedRequest(
  request,
  receipt,  // from SIWA sign-in
  signer,
  8453,
);

const response = await fetch(signedRequest);

Environment Variables

BANKR_API_KEY=your-bankr-api-key

Already using Bankr?

If your agent already uses Bankr's OpenClaw trading skill for swaps, bridges, or DeFi, this signer lets you add SIWA authentication on top — same API key, same wallet, no extra setup. Bankr's trading skill handles what your agent does; the SIWA signer handles how your agent proves who it is.