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AI agent marketplaces often connect wallets to a web dashboard long before an agent makes an on-chain payment. Login is a separate trust boundary from spending authorization. ERC-4361, Sign-In with Ethereum, standardizes an off-chain authentication message with a domain, chain, nonce and session details. ERC-1271 gives smart-contract accounts a way to validate signatures. Combining them correctly requires more than showing a signature popup: a dashboard must prevent replay, scope sessions and avoid implying that signing in authorizes trades or tool execution.
Distinguish connection, authentication and authority
Connecting a wallet only reveals an account address and supported network information. Signing a SIWE message can authenticate control of that address within a defined context. Neither action proves the wallet’s owner is a trustworthy AI operator, or that the user consents to buy services. Treat a logged-in agent dashboard as an ordinary web session with its own permissions, expiry and audit records. The application should ask for further explicit confirmation before moving funds, installing an agent plugin or disclosing confidential data. ERC-4361 was created in October 2021 for standardized Ethereum sign-in messages, not as a blanket authorization language for every possible action. Clearly distinguish authentication text from contract transaction requests in both product copy and event logs.
Verify origin and domain rather than trusting the client
Generate the SIWE challenge on the server, bind it to the intended origin and record a short-lived unique nonce. The server must reject a signed message whose domain, chain identifier, issued-at field or expiration does not match the expected policy. Do not allow the browser to choose these constraints unilaterally. Store nonce consumption atomically and reject a second use, including a replay through another device. A typed address pasted into a form is not proof that the account signed the challenge. For a multi-tenant agent marketplace, include the tenant-specific audience in the session binding so an attacker cannot reuse the login across different administrative organizations. Review deep links and redirects as part of the origin model, especially on mobile wallets.
Support ERC-1271 contract-based accounts
Externally owned accounts validate ECDSA signatures differently from smart-contract wallets. ERC-1271, created in July 2018, standardizes a contract method for assessing whether a message hash and signature are valid. A service that supports contract wallets should call the appropriate validation route rather than assuming every address has an externally recoverable public key. Validity can depend on mutable contract state or a multisignature policy, so the team should define whether to recheck long-running sessions after ownership or signer changes. A success result at login does not mean every future call remains authorized. Test a contract account whose signing policy changes after the SIWE session starts and ensure the application can revoke or revalidate sensitive permissions.
Scope sessions to the minimum administrative action
Issue an application session with a short, documented lifetime and the minimum claims needed for the dashboard. Separate ordinary browsing from publishing an AI agent, modifying settlement destinations and moving funds. Do not put a permanent API secret into the SIWE message. Store server-side revocation state, rotate session tokens after recovery and expire all sessions after confirmed account compromise. A dashboard for managing autonomous tools should show the exact permissions it grants, including external calls or scheduled jobs. If a user changes wallet address, do not silently transfer access to the old organization or assume both identities control the same agent. A fresh challenge may be necessary for elevated administrative changes.
Test replay, phishing and account transitions
Build a test matrix around reused nonces, mismatched domains, expired messages, clock drift, wrong chain IDs, redirect manipulation and repeated signature prompts. Include a wallet that has no signer for the requested address and a contract wallet that returns an invalid ERC-1271 result. Display human-readable domain and action context so a user can spot a suspicious request. A session created from one approved signature should not be reusable as a payment order. Capture signed-message metadata and server verification outcomes for audit, but do not store wallet seed phrases or request them from users. Use adversarial tests to identify cases where one browser session can take control of another tenant’s AI agent profile.
Design a transparent separation of trust layers
The wallet proves address control under the authentication rules. The marketplace may separately verify legal business information, creator consent, software integrity, customer complaints and settlement history. Display these as distinct claims rather than merging them into one verified badge. Support operators should be able to revoke marketplace roles while preserving the underlying wallet’s ownership. For an agent performing business actions, require a separate scoped execution credential after dashboard login, with tight expiration and spend limits. A secure user experience does not pretend that decentralized authentication removes the need for account recovery, dispute resolution or role-based authorization. It makes each assumption legible and testable.
ERC-4361 and ERC-1271 help a Web3 AI service authenticate diverse wallets, but they are components of a broader access-control architecture. Keeping session authentication separate from transactional authority is the most important design boundary.
