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Demo

Getting Started with Spend Permissions

This guide will walk you through a simple example of building an app that leverages Spend Permissions using OnchainKit, Viem and Wagmi.

A complete example of this demo can be found here.
Smart contract deployment addresses for SpendPermissionManager.sol can be found here.

Set up a basic app template using OnchainKit

Set up a boilerplate React/Next app by running the following command and following the instructions. Don't worry about getting a Coinbase Developer Platform API Key, you don't need one for this example. When prompted to use Coinbase Smart Wallet select "yes".

npm create onchain@latest

This will generate an app that is ready to run and contains a wallet connection button that users can use to connect their smart wallet to the application.

From here, we'll modify the app to assemble, sign, approve and use a spend permission to spend our users' funds!

Set up your spender wallet

Add the following variables to your .env:

SPENDER_PRIVATE_KEY=
NEXT_PUBLIC_SPENDER_ADDRESS=

Our spender will need to sign transactions from our app, so we'll create a wallet (private key and address) for our spender. If you have Foundry installed, you can generate a new wallet via cast wallet new. If you already have a development keypair you can use that too. Assign the private key and address to SPENDER_PRIVATE_KEY and NEXT_PUBLIC_SPENDER_ADDRESS, respectively.

Create a spender client

Our client is what our app will use to communicate with the blockchain.

Create a sibling directory to app called lib and add the following spender.ts file to create your spender client.

lib/spender. ts
import { createPublicClient, createWalletClient, Hex, http } from "viem";
import { baseSepolia } from "viem/chains";
import { privateKeyToAccount } from "viem/accounts";
 
export async function getPublicClient() {
  const client = createPublicClient({
    chain: baseSepolia,
    transport: http(),
  });
  return client;
}
 
export async function getSpenderWalletClient() {
  const spenderAccount = privateKeyToAccount(
    process.env.SPENDER_PRIVATE_KEY! as Hex
  );
 
  const spenderWallet = await createWalletClient({
    account: spenderAccount,
    chain: baseSepolia,
    transport: http(),
  });
  return spenderWallet;
}

Configure the Smart Wallet URL

In app/providers.tsx, update the value of keysUrl to be "https://keys-dev.coinbase.com/connect". This will point your app to connect to our public dev environment for smart wallet connections.

We also want to point our chain id to Base Sepolia testnet by setting replacing all instances of base with baseSepolia in this file (including the import).

Your config in app/providers.tsx should now look like this:

const config = createConfig({
  chains: [baseSepolia],
  connectors: [
    coinbaseWallet({
      appName: process.env.NEXT_PUBLIC_ONCHAINKIT_PROJECT_NAME,
      preference: process.env.NEXT_PUBLIC_ONCHAINKIT_WALLET_CONFIG as
        | "smartWalletOnly"
        | "all",
      // @ts-ignore
      keysUrl: "https://keys-dev.coinbase.com/connect"
    }),
  ],
  storage: createStorage({
    storage: cookieStorage,
  }),
  ssr: true,
  transports: {
    [baseSepolia.id]: http(),
  },
});

Set up our interface to the SpendPermissionManager smart contract

Spend permissions are managed by a singleton contract called the SpendPermissionManager. We'll add some configuration so our client knows how to interact with this contract.

Inside your /lib directory, create a new subdirectory called /abi. This is where we'll store information about smart contract interfaces and addresses.

Add a new file called SpendPermissionManager.ts and copy and paste the code from this file.

Add a Subscribe button

Let's create a button that will prompt a user to subscribe to our services by authorizing a spend permission for our app to spend their assets.

Create a subdirectory inside /app called /components and paste the following code into a new file called Subscribe.tsx.

We'll walk through what's happening here in subsequent steps.

"use client";
import { cn, color, pressable, text } from "@coinbase/onchainkit/theme";
import { useEffect, useState } from "react";
import {
  useAccount,
  useChainId,
  useConnect,
  useConnectors,
  useSignTypedData,
} from "wagmi";
import { Address, Hex, parseUnits } from "viem";
import { useQuery } from "@tanstack/react-query";
import { spendPermissionManagerAddress } from "@/lib/abi/SpendPermissionManager";
 
export default function Subscribe() {
  const [isDisabled, setIsDisabled] = useState(false);
  const [signature, setSignature] = useState<Hex>();
  const [transactions, setTransactions] = useState<Hex[]>([]);
  const [spendPermission, setSpendPermission] = useState<object>();
 
  const { signTypedDataAsync } = useSignTypedData();
  const account = useAccount();
  const chainId = useChainId();
  const { connectAsync } = useConnect();
  const connectors = useConnectors();
 
  const { data, error, isLoading, refetch } = useQuery({
    queryKey: ["collectSubscription"],
    queryFn: handleCollectSubscription,
    refetchOnWindowFocus: false,
    enabled: !!signature,
  });
 
  async function handleSubmit() {
    setIsDisabled(true);
    let accountAddress = account?.address;
    if (!accountAddress) {
      try {
        const requestAccounts = await connectAsync({
          connector: connectors[0],
        });
        accountAddress = requestAccounts.accounts[0];
      } catch {
        return;
      }
    }
 
    const spendPermission = {
      account: accountAddress, // User wallet address
      spender: process.env.NEXT_PUBLIC_SPENDER_ADDRESS! as Address, // Spender smart contract wallet address
      token: "0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE" as Address, // ETH (https://eips.ethereum.org/EIPS/eip-7528)
      allowance: parseUnits("10", 18),
      period: 86400, // seconds in a day
      start: 0, // unix timestamp
      end: 281474976710655, // max uint48
      salt: BigInt(0),
      extraData: "0x" as Hex,
    };
 
    try {
      const signature = await signTypedDataAsync({
        domain: {
          name: "Spend Permission Manager",
          version: "1",
          chainId: chainId,
          verifyingContract: spendPermissionManagerAddress,
        },
        types: {
          SpendPermission: [
            { name: "account", type: "address" },
            { name: "spender", type: "address" },
            { name: "token", type: "address" },
            { name: "allowance", type: "uint160" },
            { name: "period", type: "uint48" },
            { name: "start", type: "uint48" },
            { name: "end", type: "uint48" },
            { name: "salt", type: "uint256" },
            { name: "extraData", type: "bytes" },
          ],
        },
        primaryType: "SpendPermission",
        message: spendPermission,
      });
      setSpendPermission(spendPermission);
      setSignature(signature);
    } catch (e) {
      console.error(e);
    }
    setIsDisabled(false);
  }
 
  async function handleCollectSubscription() {
    setIsDisabled(true);
    let data;
    try {
      const replacer = (key: string, value: any) => {
        if (typeof value === "bigint") {
          return value.toString();
        }
        return value;
      };
      const response = await fetch("/collect", {
        method: "POST",
        headers: {
          "Content-Type": "application/json",
        },
        body: JSON.stringify(
          {
            spendPermission,
            signature,
            dummyData: Math.ceil(Math.random() * 100),
          },
          replacer
        ),
      });
      if (!response.ok) {
        throw new Error("Network response was not ok");
      }
      data = await response.json();
    } catch (e) {
      console.error(e);
    }
    setIsDisabled(false);
    return data;
  }
 
  useEffect(() => {
    if (!data) return;
    setTransactions([data?.transactionHash, ...transactions]);
  }, [data]);
 
  return (
    <div>
      {!signature ? (
        <div className="flex w-[450px]">
          <button
            className={cn(
              pressable.primary,
              "w-full rounded-xl",
              "px-4 py-3 font-medium text-base text-white leading-6",
              isDisabled && pressable.disabled,
              text.headline
            )}
            onClick={handleSubmit}
            type="button"
            disabled={isDisabled}
            data-testid="ockTransactionButton_Button"
          >
            <span
              className={cn(
                text.headline,
                color.inverse,
                "flex justify-center"
              )}
            >
              Subscribe
            </span>
          </button>
        </div>
      ) : (
        <div className="space-y-8 w-[450px]">
          <div className="flex">
            <button
              className={cn(
                pressable.primary,
                "w-full rounded-xl",
                "px-4 py-3 font-medium text-base text-white leading-6",
                isDisabled && pressable.disabled,
                text.headline
              )}
              onClick={() => refetch()}
              type="button"
              disabled={isDisabled}
              data-testid="collectSubscriptionButton_Button"
            >
              <span
                className={cn(
                  text.headline,
                  color.inverse,
                  "flex justify-center"
                )}
              >
                Collect Subscription
              </span>
            </button>
          </div>
          <div className="h-80 space-y-4 relative">
            <div className="text-lg font-bold">Subscription Payments</div>
            <div className="flex flex-col">
              {transactions.map((transactionHash, i) => (
                <a
                  key={i}
                  className="hover:underline text-ellipsis truncate"
                  target="_blank"
                  href={`https://sepolia.basescan.org/tx/${transactionHash}`}
                >
                  View transaction {transactionHash}
                </a>
              ))}
            </div>
          </div>
        </div>
      )}
    </div>
  );
}

Also be sure to add this new Subscribe button component to the top level component in page.tsx. You can delete lines 77-127 and put your button there.

page.tsx
  ...
      <main className="flex-grow flex items-center justify-center">
        <div className="max-w-4xl w-full p-4">
          <div className="w-1/3 mx-auto mb-6">
            <ImageSvg />
          </div>
          <div className="flex justify-center mb-6">
            <Subscribe />
          </div>
        </div>
      </main>
  ...

Examine the SpendPermission object our user will sign

A SpendPermission is the struct that defines the parameters of the permission. See the solidity struct here.

You can see the spend permission object being defined in lines 49-59 of our Subscribe component:

Subscribe.tsx
 
export default function Subscribe() {
...
 
  async function handleSubmit() {
    setIsDisabled(true);
    let accountAddress = account?.address;
    if (!accountAddress) {
      try {
        const requestAccounts = await connectAsync({
          connector: connectors[0],
        });
        accountAddress = requestAccounts.accounts[0];
      } catch {
        return;
      }
    }
 
    // Define a `SpendPermission` to request from the user
    const spendPermission = {  
      account: accountAddress, // User wallet address
      spender: process.env.NEXT_PUBLIC_SPENDER_ADDRESS! as Address, // Spender smart contract wallet address
      token: "0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE" as Address, // ETH (https://eips.ethereum.org/EIPS/eip-7528)
      allowance: parseUnits("10", 18), 
      period: 86400, // seconds
      start: 0, // unix time, seconds
      end: 281474976710655, // max uint48
      salt: BigInt(0), 
      extraData: "0x" as Hex, 
    }; 
  }
    ...
 
  return (
    <div>
      ...
    </div>
  );
}

Observe the signTypedData hook

As part of our button handler handleSubmit, in lines 61-91 of our subscribe component we call signTypedDataAsync, a Wagmi hook that will prompt our user to create a signature from their wallet across the details of the spend permission.

Subscribe.tsx
 
export default function Subscribe() {
  ...
 
  async function handleSubmit() {
    ...
 
    // Obtain signature over `SpendPermission` from user
    try {
      const signature = await signTypedDataAsync({ 
        domain: { 
          name: "Spend Permission Manager", 
          version: "1", 
          chainId: chainId, 
          verifyingContract: spendPermissionManagerAddress, 
        }, 
        types: { 
          SpendPermission: [ 
            { name: "account", type: "address" }, 
            { name: "spender", type: "address" }, 
            { name: "token", type: "address" }, 
            { name: "allowance", type: "uint160" }, 
            { name: "period", type: "uint48" }, 
            { name: "start", type: "uint48" }, 
            { name: "end", type: "uint48" }, 
            { name: "salt", type: "uint256" }, 
            { name: "extraData", type: "bytes" }, 
          ], 
        }, 
        primaryType: "SpendPermission", 
        message: spendPermission, 
      }); 
      setSpendPermission(spendPermission); 
      setSignature(signature); 
    } catch (e) {
      console.error(e)
    }
    setIsDisabled(false);
  }
 
    ...
 
  return (
    <div>
      ...
    </div>
  );
}

Approve the spend permission onchain

Now that we have a signature from the user, we can approve the permission onchain by submitting the signature and the permission details to approveWithSignature on the SpendPermissionManager contract.

Our handleCollectSubscription function that's defined in our Subscribe will pass this signature and data to our backend, so the spender client we created earlier can handle our onchain calls.

Subscribe.tsx
// We send the permission details and the user signature to our backend route
async function handleCollectSubscription() {
  setIsDisabled(true);
  let data;
  try {
    const replacer = (key: string, value: any) => {
      if (typeof value === "bigint") {
        return value.toString();
      }
      return value;
    };
    const response = await fetch("/collect", {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
      },
      body: JSON.stringify(
        {
          spendPermission,
          signature,
          dummyData: Math.ceil(Math.random() * 100),
        },
        replacer
      ),
    });
    if (!response.ok) {
      throw new Error("Network response was not ok");
    }
    data = await response.json();
  } catch (e) {
    console.error(e);
  }
  setIsDisabled(false);
  return data;
}

But wait, we don't have any backend routes set up yet! Let's define what should happen when we want to approve and use our spend permission.

Create a new subdirectory under /app called collect. Create a new file there called route.tsx and paste the following code:

route.tsx
import { NextRequest, NextResponse } from "next/server";
import { getPublicClient, getSpenderWalletClient } from "../../lib/spender";
import {
  spendPermissionManagerAbi,
  spendPermissionManagerAddress,
} from "../../lib/abi/SpendPermissionManager";
 
export async function POST(request: NextRequest) {
  const spenderBundlerClient = await getSpenderWalletClient();
  const publicClient = await getPublicClient();
  try {
    const body = await request.json();
    const { spendPermission, signature } = body;
 
    const approvalTxnHash = await spenderBundlerClient.writeContract({
      address: spendPermissionManagerAddress,
      abi: spendPermissionManagerAbi,
      functionName: "approveWithSignature",
      args: [spendPermission, signature],
    });
 
    const approvalReceipt = await publicClient.waitForTransactionReceipt({
      hash: approvalTxnHash,
    });
 
    const spendTxnHash = await spenderBundlerClient.writeContract({
      address: spendPermissionManagerAddress,
      abi: spendPermissionManagerAbi,
      functionName: "spend",
      args: [spendPermission, "1"],
    });
 
    const spendReceipt = await publicClient.waitForTransactionReceipt({
      hash: spendTxnHash,
    });
 
    return NextResponse.json({
      status: spendReceipt.status ? "success" : "failure",
      transactionHash: spendReceipt.transactionHash,
      transactionUrl: `https://sepolia.basescan.org/tx/${spendReceipt.transactionHash}`,
    });
  } catch (error) {
    console.error(error);
    return NextResponse.json({}, { status: 500 });
  }
}

This code is using our spender client to do two things:

  1. calls approveWithSignature to approve the spend permission
  2. calls spend to make use of our allowance and spend our user's funds

Try out your app

Run your app locally with npm run dev and visit localhost:3000.

When you click the "Subscribe" button you should be prompted to create or connect your Smart Wallet.

You can create a new Smart Wallet via the popup. Note that you'll need a little ETH in this wallet to fund the deployment of your account. If you don't have any testnet ETH, try this Coinbase faucet.

Note that we'll need a little bit of base sepolia ETH in both wallet addresses (the "user" wallet and the "app" wallet). In a more involved implementation you would use a paymaster to eliminate this requirement. For now, If you don't have any base sepolia ETH, try this Coinbase faucet.

Once your wallet is created and both wallets are funded, return to the app and click "Subscribe", then sign the prompt to allow the spend permission.

Once you've subscribed, you should see a spend transaction hash show up on screen after a few seconds. You can prompt subsequent spends by clicking the "Collect Subscription" button. Click the transactions to check them out on Etherscan!

We've made it! 🎉

Our app successfully

  • prompts the user to connect their Coinbase Smart Wallet to our app
  • assembles a spend permission representing our recurring spending needs as an app
  • retrieves a signature from the user authorizing this spend permission
  • approves the spend permission onchain
  • uses this permission to retrieve user assets within our allowance