Sessions

Sessions can be used to send transactions from a dapp on behalf of a user without requiring their confirmation with a wallet.

The user is guaranteed that the dapp can only execute transactions that comply to the policies of the session and until the session expires.

Installation

npm install @argent/x-sessions
# or
pnpm add @argent/x-sessions

Demo Dapp

A demo dapp using both sessions and offchain sessions can be found here https://github.com/argentlabs/session-keys-example-dapp

Session keys

Creating an Argent session account

First you need to have a deployed account. This is the account that will authorise the session and interact with the contracts of your dapp.

To sign the session message the method needed is openSession. After the user sign the message, a session account can be created using buildSessionAccount.

This example session will allow the dapp to execute an example endpoint on an example contract without asking the user to approve the transaction again. After signing the session the dapp can execute all transactions listed in allowedMethods whenever it wants and as many times as it wants.

The list of allowedMethods needs to be communicated with Argent, in order to be whitelisted.

export interface AllowedMethod {
  "Contract Address": string
  selector: string
}

export type MetadataTxFee = {
  tokenAddress: string
  maxAmount: string
}

export type SessionMetadata = {
  projectID: string
  txFees: MetadataTxFee[]
  projectSignature?: Signature
}

type SessionParams = {
  dappKey?: Uint8Array // this is optional. This sdk generate a dappKey using ec.starkCurve.utils.randomPrivateKey() if not provided
  allowedMethods: AllowedMethod[]
  expiry: bigint
  metaData: SessionMetadata
}

The following snippet show how to create and use a session account

import {
  SignSessionError,
  SessionParams,
  openSession,
  buildSessionAccount
} from "@argent/x-sessions"
import { ec } from "starknet"

const sessionParams: SessionParams = {
  allowedMethods: [
    {
      "Contract Address": contractAddress,
      selector: "method_selector"
    }
  ],
  expiry: Math.floor(
    (Date.now() + 1000 * 60 * 60 * 24) / 1000
  ) as any, // ie: 1 day
  dappKey: ec.starkCurve.utils.randomPrivateKey(),
  metaData: {
    projectID: "test-dapp",
    txFees: [
      {
        tokenAddress: ETHTokenAddress,
        maxAmount: parseUnits("0.1", 18).value.toString()
      }
    ]
  }
}

// open session and sign message
const accountSessionSignature = await openSession({
  wallet, // StarknetWindowObject
  sessionParams, // SessionParams
  chainId // StarknetChainId
})

// create the session account from the current one that will be used to submit transactions
const sessionRequest = createSessionRequest(
  sessionParams.allowedMethods,
  sessionParams.expiry,
  sessionParams.metaData,
  sessionParams.dappKey
)

const sessionAccount = await buildSessionAccount({
  useCacheAuthorisation: false, // optional and defaulted to false, will be added in future developments
  accountSessionSignature: stark.formatSignature(
    accountSessionSignature
  ),
  sessionRequest,
  chainId, // StarknetChainId
  provider: new RpcProvider({
    nodeUrl: "https://starknet-sepolia.public.blastapi.io/rpc/v0_7",
    chainId: constants.StarknetChainId.SN_SEPOLIA
  }),
  address, // account address
  dappKey
})

try {
  const tx = sessionAccount.execute({
    // lets assume this is a erc20 contract
    contractAddress: "0x...",
    selector: "transfer",
    calldata: [
      "0x..."
      // ...
    ]
  })
} catch (e) {
  console.error((e as SignSessionError).cause, e.message)
}

Execute from outside

Executing transactions “from outside” allows an account to submit transactions on behalf of a user account, as long as they have the relevant signatures.

This package expose a method in order to get the Call required to perform an execution from outside.

// instantiate argent session service
const beService = new ArgentSessionService(
  dappKey.publicKey,
  accountSessionSignature
)

// instantiate dapp session service
const sessionDappService = new SessionDappService(
  beService,
  chainId,
  dappKey
)

// example for creating the calldata
const erc20Contract = new Contract(
  Erc20Abi as Abi,
  ETHTokenAddress,
  sessionAccount as any
)
const calldata = erc20Contract.populate("transfer", {
  recipient: address,
  amount: parseInputAmountToUint256(amount)
})

// get execute from outside data
const { contractAddress, entrypoint, calldata } =
  await sessionDappService.getOutsideExecutionCall(
    sessionRequest,
    stark.formatSignature(accountSessionSignature),
    false,
    [calldata],
    address, // the account address
    chainId,
    shortString.encodeShortString("ANY_CALLER"), // Optional: default value ANY_CALLER
    execute_after, // Optional: timestamp in seconds - this is the lower value in the range. Default value: 5 mins before Date.now()
    execute_before, // Optional: timestamp in seconds - this is the upper value in the range. Default value: 20 mins after Date.now()
    nonce: BigNumberish, // Optional: nonce, default value is a random nonce
  )

Another account can then use object { contractAddress, entrypoint, calldata } to execute the transaction.