Authenticate users

Connect and manage user wallet sessions in your Wagmi or Vanilla JavaScript dapp. With the SDK, you can:

• Connect users' wallets to your dapp.
• Access user accounts (addresses).
• Connect and sign in a single user interaction.
• Handle connection states (connected/disconnected).
• Listen for account changes in real time.
• Manage wallet sessions (connect/disconnect).
• Support multiple wallet types (extension, mobile app).

Use Wagmi

Wagmi provides a simple, hook-based approach for handling wallet connections. For example:

Handle wallet connections

import { useAccount, useConnect, useDisconnect } from "wagmi"

function ConnectWallet() {
  const { address, isConnected } = useAccount()
  const { connectors, connect, isPending } = useConnect()
  const { disconnect } = useDisconnect()

  if (isConnected) {
    return (
      <div>
        <div>Connected to {address}</div>
        <button onClick={() => disconnect()}>Disconnect</button>
      </div>
    )
  }

  return (
    <div>
      {connectors.map((connector) => (
        <button
          key={connector.uid}
          onClick={() => connect({ connector })}
          disabled={isPending}
        >
          {isPending ? "Connecting..." : `Connect ${connector.name}`}
        </button>
      ))}
    </div>
  )
}

Wagmi provides a dedicated hook for handling account lifecycle events:

import { useAccountEffect } from "wagmi"

function WatchAccount() {
  useAccountEffect({
    onConnect(data) {
      console.log("Connected!", {
        address: data.address,
        chainId: data.chainId,
        isReconnected: data.isReconnected
      })
    },
    onDisconnect() {
      console.log("Disconnected!")
    }
  })
  
  return <div>Watching for account changes...</div>
}

Use Vanilla JavaScript

You can implement user authentication directly in Vanilla JavaScript, using the eth_requestAccounts RPC method and accountsChanged provider event. For example:

import { MetaMaskSDK } from "@metamask/sdk";

// Initialize SDK
const MMSDK = new MetaMaskSDK();
const provider = MMSDK.getProvider();

// Connect wallet
async function connectWallet() {
  try {
    // Disable button while request is pending
    document.getElementById("connectBtn").disabled = true;
    
    const accounts = await provider.request({ 
      method: "eth_requestAccounts" 
    });
    
    const account = accounts[0];
    console.log("Connected:", account);
    
    // Update UI
    document.getElementById("status").textContent = `Connected: ${account}`;
    document.getElementById("connectBtn").style.display = "none";
    document.getElementById("disconnectBtn").style.display = "block";
  } catch (err) {
    if (err.code === 4001) {
      console.log("User rejected connection");
    } else {
      console.error(err);
    }
  } finally {
    document.getElementById("connectBtn").disabled = false;
  }
}

// Disconnect wallet
async function disconnectWallet() {
  try {
    await MMSDK.terminate()
  } catch (err) {
    console.error("Error with disconnecting:", err)
  }
}

// Handle account changes
provider.on("accountsChanged", (accounts) => {
  if (accounts.length === 0) {
    // User disconnected
    document.getElementById("status").textContent = "Not connected";
    document.getElementById("connectBtn").style.display = "block";
    document.getElementById("disconnectBtn").style.display = "none";
  } else {
    // Account changed
    document.getElementById("status").textContent = `Connected: ${accounts[0]}`;
  }
});

Display connect and disconnect buttons in HTML:

<div>
  <div id="status">Not connected</div>
  <button id="connectBtn" onclick="connectWallet()">Connect MetaMask</button>
  <button id="disconnectBtn" style="display: none" onclick="disconnectWallet()">
    Disconnect
  </button>
</div>

Connect and sign

If you're not using Wagmi, you can access MetaMask SDK's connectAndSign method, which requests wallet access and signs the message in a single user interaction. For example:

import { MetaMaskSDK } from "@metamask/sdk"

const MMSDK = new MetaMaskSDK()
const provider = MMSDK.getProvider()

async function handleConnectAndSign() {
  try {
    const signature = await MMSDK.connectAndSign({ msg: "Hello in one go!" })
    console.log("Signature:", signature)
  } catch (err) {
    console.error("Error with connectAndSign:", err)
  }
}

document
  .getElementById("connectSignBtn")
  .addEventListener("click", handleConnectAndSign)

The following HTML displays a Connect & Sign button:

<button id="connectSignBtn">Connect & Sign</button>

tip

This one-step flow is unique to MetaMask SDK's connectAndSign method. It's not part of Wagmi or other wallet libraries.

Best practices

Follow these best practices when authenticating users.

User interaction

• Only trigger connection requests in response to user actions (like selecting a button).
• Never auto-connect on page load.
• Provide clear feedback during connection states.

Error handling

• Handle common errors like user rejection (code 4001).
• Provide clear error messages to users.
• Fall back gracefully when MetaMask is not installed.

Account changes

• Always listen for account changes.
• Update your UI when accounts change.
• Handle disconnection events.

Chain support

• Listen for network/chain changes.
• Verify the current chain meets your requirements.
• Provide clear messaging when users need to switch networks.

Learn how to manage networks.

Common errors

The following table lists common authentication errors and their codes:

Error code	Description	Solution
4001	User rejected request	Show a message asking the user to approve the connection.
-32002	Request already pending	Disable the connect button while the request is pending.
-32603	Internal JSON-RPC error	Check if MetaMask is properly installed.

Next steps

See the following guides to add more functionality to your dapp:

• Manage networks
• Handle transactions
• Interact with smart contracts