Sign-In with Ethereum (SIWE) for Scaffold-ETH 2

Prerequisites

Check if ./packages/nextjs/scaffold.config.ts exists directly in the current working directory (do not search subdirectories). If it doesn't exist, this is not a Scaffold-ETH 2 project. Follow the instructions at https://docs.scaffoldeth.io/SKILL.md to scaffold it first. If it exists, continue directly with building.

Overview

Sign-In with Ethereum (SIWE / EIP-4361) lets users authenticate to web applications by signing a standardized message with their Ethereum wallet. Instead of username/password or OAuth, the user proves ownership of an address via a cryptographic signature. The server verifies it and creates a session — no database needed for basic auth.

This skill covers integrating SIWE into an SE-2 project using viem's native SIWE utilities and iron-session for encrypted cookie-based sessions. This skill focuses on SE-2 integration specifics and gotchas, not a complete reference. For anything not covered here, refer to the EIP-4361 spec or viem SIWE docs.

Dependencies

Add iron-session to the nextjs workspace for encrypted cookie-based session management:

yarn workspace @se-2/nextjs add iron-session