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Sign Transactions and Delegate Actions

Once users are authenticated, you can request signatures for NEAR transactions. For detailed API reference, see the Browser SDK Signer or React SDK Signer documentation.

Get a Signer​

After login, obtain a signer instance:

const signer = await client.getSigner();

The signer is used to request signatures and interact with the FastAuth contracts. Learn more about the signing architecture.

Request a Transaction Signature​

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When using requestTransactionSignature or requestDelegateActionSignature, be aware that these methods may trigger a browser redirection or open a pop-up window, depending on the SDK and the authentication provider you have integrated. Make sure to design your app's UX to handle and inform users about these context switches appropriately.

To sign a transaction, create the transaction and request user approval:

import { transactions } from "near-api-js";

// Build your transaction
const transaction = transactions.createTransaction(
  "sender.testnet",           // Sender account
  publicKey,                  // Sender's public key
  "receiver.testnet",         // Receiver account
  nonce,                      // Account nonce
  [                           // Actions
    transactions.transfer(BigInt("1000000000000000000000000")), // 1 NEAR
  ],
  blockHash                   // Recent block hash
);

// Request signature (redirects to Auth0 for approval)
await signer.requestTransactionSignature({
  transaction,
  name: "My dApp",
  imageUrl: "https://my-dapp.com/logo.png",
  redirectUri: window.location.origin + "/callback",
});

Complete the Signing Flow​

After the user approves, retrieve the signature and send the transaction:

// On callback page, get the signature request
const signatureRequest = await signer.getSignatureRequest();

// Create the sign action for the FastAuth contract
const signAction = await signer.createSignAction(signatureRequest, {
  gas: 300000000000000n,
  deposit: 1n,
});

// Build and send the transaction to FastAuth
// The FastAuth contract will verify the JWT and return an MPC signature

For more details on how the FastAuth contract processes signatures, see the FastAuth Contract documentation.

Request a Delegate Action Signature​

For meta-transactions (gasless transactions), use delegate actions:

import { buildDelegateAction } from "near-api-js/lib/transaction";

const delegateAction = buildDelegateAction({
  senderId: "sender.testnet",
  receiverId: "receiver.testnet",
  actions: [
    transactions.transfer(BigInt("1000000000000000000000000")),
  ],
  publicKey,
  nonce,
  maxBlockHeight,
});

// Request delegate action signature
await signer.requestDelegateActionSignature({
  delegateAction,
  name: "My dApp",
  imageUrl: "https://my-dapp.com/logo.png",
});

Get the User's Public Key​

Retrieve the user's derived public key for building transactions:

// Get the Ed25519 public key (default)
const publicKey = await signer.getPublicKey();

// Or specify an algorithm
const secp256k1Key = await signer.getPublicKey("secp256k1");

The public key is derived from the user's authentication path using the MPC network.