Paying for Another Account's Signature Using Solana Chain Signatures

Let's walk through a scenario where one wallet handles transaction fees while another account makes a signature request using the Solana Chain Signatures Contract. This setup is common when an app or service covers fees for users.

Setting up the Scenario

First, you'll set up your connection to Solana using a wallet that will pay for the transaction fees (fee payer).

Next, you'll generate a new account for the requester—the user or service asking for a signature. This requester will initiate the request but won't handle any transaction fees.

With your fee payer and requester ready, you'll configure the Chain Signature Contract to clearly specify who's making the request and who's paying the fees.

Finally, you'll make the actual request for the signature. The fee payer's wallet will automatically cover the fees, while the requester account will be the signer of the request.

Example Walkthrough

First, create a connection to Solana and set up your wallet as the fee payer:

const connection = new Connection('https://api.devnet.solana.com', 'confirmed')
const privateKeyString = process.env.SOLANA_PRIVATE_KEY!
const privateKey = JSON.parse(privateKeyString)
const feePayerWallet = new Wallet(
  Keypair.fromSecretKey(new Uint8Array(privateKey))
)
const provider = new AnchorProvider(
  connection,
  feePayerWallet,
  AnchorProvider.defaultOptions()
)

Then, generate a requester account:

const requester = Keypair.generate()

Next, initialize your Chain Signature Contract:

const chainSigContract = new contracts.solana.ChainSignatureContract({
  provider,
  programId: 'ChainSignatureProgramIdHere',
  requesterAddress: requester.publicKey.toString(),
})

Now, directly call the sign method on your Chain Signature Contract, specifying the requester details in remainingAccounts and their keypair in remainingSigners:

const signature = await chainSigContract.sign(
  {
    path: 'example_path',
    payload: Array(32).fill(1),
    key_version: 0,
  },
  {
    remainingAccounts: [
      { pubkey: requester.publicKey, isSigner: true, isWritable: false },
    ],
    remainingSigners: [requester],
  }
)
 
console.log('Received signature:', signature)

Complete Example

Here's the full example for quick reference:

import { Connection, Keypair } from '@solana/web3.js'
import { AnchorProvider, Wallet } from '@coral-xyz/anchor'
import { contracts, RSVSignature } from 'signet.js'
 
const connection = new Connection('https://api.devnet.solana.com', 'confirmed')
const privateKeyString = process.env.SOLANA_PRIVATE_KEY!
const privateKey = JSON.parse(privateKeyString)
const feePayerWallet = new Wallet(
  Keypair.fromSecretKey(new Uint8Array(privateKey))
)
const provider = new AnchorProvider(
  connection,
  feePayerWallet,
  AnchorProvider.defaultOptions()
)
 
const requester = Keypair.generate()
 
const chainSigContract = new contracts.solana.ChainSignatureContract({
  provider,
  programId: 'ChainSignatureProgramIdHere',
  requesterAddress: requester.publicKey.toString(),
})
 
;(async () => {
  try {
    const signature = await chainSigContract.sign(
      {
        path: 'example_path',
        payload: Array(32).fill(1),
        key_version: 0,
      },
      {
        remainingAccounts: [
          { pubkey: requester.publicKey, isSigner: true, isWritable: false },
        ],
        remainingSigners: [requester],
      }
    )
 
    console.log('Received signature:', signature)
  } catch (error) {
    console.error('Transaction failed:', error)
  }
})()