Auth (Sign In With Base) - Base Documentation

Learn how to handle authentication flows with Privy and Base Account, including both Privy-managed authentication and custom backend verification.

Overview

Privy handles the initial authentication flow, managing user sessions and wallet connections. You can also implement additional authentication layers for enhanced security or custom requirements. The code snippets in this guide are based on the following example project:

Base Account Privy Templatehttps://github.com/base/base-account-privy

Authentication Flow

Privy manages the primary authentication before users enter your application:

Custom Authentication

For additional security or custom authentication requirements, you can implement backend verification using Sign-In with Ethereum (SIWE) with the Base Account SDK.

Setup

Follow the Setup guide to set up Privy with Base Account. We use the SignInWithBaseButton component from the @base-org/account-ui/react package to make sure we are following the brand guidelines.

"use client";

import { useState } from "react";
import { useBaseAccountSdk } from "@privy-io/react-auth";
import { SignInWithBaseButton } from "@base-org/account-ui/react";

export const Authentication = () => {
  const { baseAccountSdk } = useBaseAccountSdk();
  const [loading, setLoading] = useState(false);
  const [verificationResult, setVerificationResult] = useState<any>(null);

  const provider = baseAccountSdk?.getProvider();

  const handleSignInWithBase = async () => {
    if (!provider) return;

    try {
      setLoading(true);

      // Get a fresh nonce from backend
      const nonceResponse = await fetch("/api/auth/nonce");
      const { nonce } = await nonceResponse.json();

      // Switch to Base Chain
      await provider.request({
        method: "wallet_switchEthereumChain",
        params: [{ chainId: "0x2105" }],
      });

      // Connect and authenticate with SIWE
      const response = (await provider.request({
        method: "wallet_connect",
        params: [{
          version: "1",
          capabilities: {
            signInWithEthereum: {
              nonce,
              chainId: "0x2105",
            },
          },
        }],
      })) as {
        accounts: {
          address: string;
          capabilities: {
            signInWithEthereum: { signature: string; message: string };
          };
        }[];
      };

      const { address } = response.accounts[0];
      const { message, signature } = response.accounts[0].capabilities.signInWithEthereum;

      // Verify with backend
      const verifyResponse = await fetch("/api/auth/verify", {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({ address, message, signature }),
      });

      const result = await verifyResponse.json();
      setVerificationResult(result);
    } catch (error) {
      console.error("Sign in error:", error);
    } finally {
      setLoading(false);
    }
  };

  return (
    <div>
      <SignInWithBaseButton onClick={handleSignInWithBase} />
      {verificationResult && (
        <div>✅ Backend Verified! Address: {verificationResult.address}</div>
      )}
    </div>
  );
};

export default Authentication;

Using the Authentication Component

Add the Authentication component to your page to enable Sign In with Base functionality:

import Authentication from "@/components/sections/authentication";

export default function Home() {
  return (
    <main className="flex min-h-screen flex-col items-center justify-center p-24">
      <div className="z-10 w-full max-w-5xl items-center justify-between font-mono text-sm">
        <h1 className="text-4xl font-bold text-center mb-8">
          Base Account with Privy
        </h1>
        
        <div className="flex flex-col items-center space-y-4">
          <Authentication />
        </div>
      </div>
    </main>
  );
}

"use client";

import { usePrivy } from "@privy-io/react-auth";
import Authentication from "@/components/sections/authentication";

export default function Dashboard() {
  const { authenticated } = usePrivy();

  if (!authenticated) {
    return (
      <div className="flex min-h-screen items-center justify-center">
        <div className="text-center">
          <h1 className="text-2xl font-bold mb-4">Access Required</h1>
          <p className="mb-6">Please authenticate to access the dashboard.</p>
          <Authentication />
        </div>
      </div>
    );
  }

  return (
    <div className="min-h-screen p-8">
      <h1 className="text-3xl font-bold mb-6">Dashboard</h1>
      <p>Welcome to your authenticated dashboard!</p>
      {/* Your protected content here */}
    </div>
  );
}

Backend Implementation

Development Only: This backend implementation is not production-ready. The nonce management system needs proper persistence and security enhancements for production use.

import { NextResponse } from 'next/server';
import crypto from 'crypto';
import { nonceStore } from '@/lib/nonce-store';

export async function GET() {
  try {
    const nonce = crypto.randomBytes(16).toString('hex');
    nonceStore.add(nonce);
    
    return NextResponse.json({ nonce });
  } catch (error) {
    return NextResponse.json(
      { error: 'Failed to generate nonce' },
      { status: 500 }
    );
  }
}

import { NextRequest, NextResponse } from 'next/server';
import { createPublicClient, http } from 'viem';
import { base } from 'viem/chains';
import { nonceStore } from '@/lib/nonce-store';

const client = createPublicClient({ 
  chain: base, 
  transport: http() 
});

export async function POST(request: NextRequest) {
  try {
    const { address, message, signature } = await request.json();

    // Extract nonce from SIWE message
    const nonce = message.match(/Nonce: (\w+)/)?.[1];
    
    if (!nonce || !nonceStore.consume(nonce)) {
      return NextResponse.json(
        { error: 'Invalid or reused nonce' },
        { status: 400 }
      );
    }

    // Verify signature using viem
    const valid = await client.verifyMessage({ 
      address: address as `0x${string}`, 
      message, 
      signature: signature as `0x${string}` 
    });

    if (!valid) {
      return NextResponse.json(
        { error: 'Invalid signature' },
        { status: 401 }
      );
    }

    return NextResponse.json({ 
      success: true, 
      address,
      timestamp: new Date().toISOString()
    });

  } catch (error) {
    return NextResponse.json(
      { error: 'Internal server error' },
      { status: 500 }
    );
  }
}

// Simple in-memory nonce store
// In production, use Redis or a database
class NonceStore {
  private nonces = new Set<string>();

  add(nonce: string): void {
    this.nonces.add(nonce);
  }

  consume(nonce: string): boolean {
    return this.nonces.delete(nonce);
  }
}

export const nonceStore = new NonceStore();

Production Considerations

For production deployments, enhance the backend implementation with:

Persistent storage: Use Redis or a database instead of in-memory storage
Rate limiting: Implement request rate limiting for nonce generation
Session management: Create proper JWT tokens or session cookies
Nonce expiration: Add timestamp-based nonce expiration

​Overview

​Authentication Flow

​Custom Authentication

​Setup

​Frontend Component (Sign In With Base)

​Using the Authentication Component

​Backend Implementation

​Production Considerations

Overview

Authentication Flow

Custom Authentication

Setup

Frontend Component (Sign In With Base)

Using the Authentication Component

Backend Implementation

Production Considerations