User Authentication

Connect and manage user wallet sessions in your dApp. This guide covers both Wagmi (recommended) and vanilla JavaScript approaches.

With MetaMask SDK, you can:

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

Using Wagmi

Wagmi provides a simple, hook-based approach for handling 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>
  )
}

Handle Account Changes

Wagmi automatically handles account changes, but you can also listen for them:

import { useAccount } from 'wagmi'

function WatchAccount() {
  const { address } = useAccount({
    onConnect: ({ address }) => console.log('Connected', address),
    onDisconnect: () => console.log('Disconnected')
  })
  
  return <div>Current account: {address}</div>
}

Using Vanilla JavaScript

If you're not using React, here's how to implement authentication directly:

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;
  }
}

// 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]}`;
  }
});

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>

Best Practices

1. User Interaction

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

2. Error Handling

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

3. Account Changes

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

4. Chain Support

   • Listen for network/chain changes
   • Verify the current chain meets your requirements
   • Provide clear messaging when users need to switch networks
   • Learn more here: Network Management

Common Errors

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

Next Steps

• Network Management
• Transaction Handling
• Interact with Contracts